What do I do with an aggressive dog???

[font=arial][size=2]She growled at my sister once - but we had been fooling around and my sister punched me in the arm

It sounds like she is thinking he self as the "pack leader" of your household and showing dominance towards others in protecting her family.  I don't really know what you could do, i guess i'll leave that up to someone wiser than me in this particular case![/size][/font]

Sounds like your girl is being a very typical Chessie.  Chesapeakes are not curly labs.  They are notorious for being dog aggressive, territorial and possessive.  Get your girl fixed, get her in obedience classes, don't put her down.  Talk to someone who knows the breed- the breeder, CBRR&R, [linkhttp://www.cbrs4me.com]www.cbrs4me.com[/link].  Chances are she will never be friendly with dogs, but with training you can control her aggression.
The devotion to family and friends, yet the protectiveness and loyalty is what drew me to the breed.  She sounds like a wonderful girl who just needs some guidance.  Good luck!
[linkhttp://www.cbrrescue.org/WARNING.HTM]http://www.cbrrescue.org/WARNING.HTM[/link]
[linkhttp://www.cbrrescue.org/articles/dontbuy.htm]http://www.cbrrescue.org/articles/dontbuy.htm[/link]
[linkhttp://www.cbrrescue.org/articles/aggression.htm]http://www.cbrrescue.org/articles/aggression.htm[/link]
 
 

Thank you SO much for your reply!  You have no idea how much I needed to hear "dont put her down".  It seems like everyone is telling me it's my only option - but I can't, not for her just acting like the dog that she is.  It's up to me to keep her safe and it's up to me to keep her away from other animals.  I've been sick worrying about this and am happy to hear that Chesapeakes are like that and it's not just her.  I got her from an uncle who breeds them as a house-warming gift and didn't know much about Chessie's beforehand (At first I did think they were 'curly labs').  He has since moved away and we haven't been in touch so I couldn't talk to him.  Thank you for the links too - they are very helpful.  I will get her fixed and take her to obedience classes - along with putting the dog run and kennel in our yard. 

I hope no one will slam me for this, as I am a spay/neuter advocate, but there is at least some scientific evidence that spaying a female does not reduce dog to dog aggression as neutering does in males, and, in fact, may worsen it. 
The first thing you should do is consult a really qualified behaviorist - if you don't know where to find one, you can try calling the nearest teaching veterinary school for a referral.  You need a pro who can evaluate her in person, since it is often the case that some dogs are only aggressive behind a barrier or on lead, and are fine off lead - even Chessies (who do have a reputation for being dog aggressive, as another poster suggested).  Until then, this is not a dog I would let run the fence line, or see out the picture window.  Block those views so she isn't "practicing" bad behavior. 

Another thing:  It came out last year that aggression in dogs can be caused/triggered by a low thyroid -- even just a slightly low thyroid. 
 
Just slightly low thyroid levels can affect dogs in different ways.  My boy is not aggressive; however, he loses "patches" of hair which the vets totally believe is contact allergens.  I do not believe this is true at all.   We tested his thyroid, and he was "within" range -- so the vet didn't want to treat.  On the fence about it, I agreed not to treat.  It is notable that his levels were on the low side within the range.  At about 40 %.     ........Then, after the trauma of being neutered (no, normally, it's not traumatic -- but for a dog with low thyroid, any stressful event can "trigger" body changes), well then he started to lose major areas of hair.    The vet still thought it was allergies.  [sm=uhoh.gif].   Well, I asked for the meds.  Gee, his hair started growing back...........    Yes, I could be wrong.  I am leaving out a bit of other information,  but I don't think I am wrong about the low thryoid playing a big factor in the whole deal.
 
Thyroid is really tricky.  It's the major player in all body functions.  Too high or too low a level is bad, either way.  It's a constant balancing act, but can make a huge difference if there is a problem and it gets straightened out.
 
When you do the testing:  get your vet to send it to Michigan State University.  Warning: they require lots of blood.  Like 3 tubes of the blood after it has been spun down.  Get your vet to make sure they know exactly how much to send.  MSU requires more blood than other labs.  With a case as serious as yours --if this is a contributing factor - then you don't want to mess around and send the bloodwork to a regular lab.  Really.  The other option is to send it directly to Dr. Dodds - but you have to package it yourself with some cool/freezer packs so that it will stay cold -- but not frozen! And then ship overnight to her lab in California.  It's a bit of a headache - but it's doable. (google Dr. Dodds).  But, only use one of these two labs  -=--especially for this initial testing.       ((( If your dog does start these meds, then re-testing has to be done 4 - 6 hours after dosage))).  But, the original testing can be taken anytime during the day.
 
I realize it's been going on for 3 years, but I would still check this out as a possible contributing factor.  Lots of doctors and vets don't realize how important the thryoid is to the entire body unless they themselves have been thru issues that didn't fit the "textbook" guidelines.  I've learned in my life that lots of problems don't have the symptoms that they are "supposed to have", according to the "textbooks".   Real life doesn't necessarily follow those darn textbooks! 
 
  Which leads me to another subject, that I just thought of.  I would also consider putting her on a homemade diet to determine if she has food allergies.  Monica Segal has a book that talks a bit about this.  It's an "elimination" diet.  NOPE, she doesn't express "normal" signs of food allergies---> ie, itchy skin, biting the paws, dull coat, etc.  Her problem is aggression.  But think about all those human children that have problems with ADHD.  Some of those poor mom's can't get their children to behave nicely -- some of them really act out very meanly towards other children. Some kids start fights with other kids.  It can be a real problem.   You know what they have to do?  One of the things is to cut out lots of food types - espcially gluten type foods.  So, yep, her problem can also be food related. So, I would start her on a proper elimination diet as well.    I would give her a little bit of top quality fish oil (I use Carlsons-for humans. I give about 1/4 tsp).  I don't want to do too much oil in a day.    I would also give a good, human grade multi-B vitamin. My guys get 25mg at each meal.  This can help them to "handle" stress.  I use it myself!  I do not give Vit E or Vit C.   Basically just the multi B and fish oils.  And, when giving home cooked meals for an extended period of time, you do need to give Calcium.  I use a calcium/magnesium  2 to 1 ratio --> however, you can also use dried egg shells. Lot's of people and several books I have mention this.  It will require a little bit of reading on this subject ( I'm still learning), but it also may make a big difference.   Good luck with your baby.
 
 

What Chasza said.  The very first thing you need to do is to go to the vet and see if there is anything physically wrong.  And request a COMPLETE thyroid pannel.  Aggression is a symptom of low thyroid.  You can look up Dodman's books and articles (or Dodd's articles) for more info.  Please do not agree to an inhouse test.  MSU or Hemopet (Dr Dodds).  Dr Dodds is more than happy to talk to people about test results, even if you didn't use her lab.
 
Then find a good behaviorist and you may want to look into a book called "Click to Calm". 

Again, it is very,very typical of a Chesapeake to become dog aggressive even if they were previously socialized with other dogs at an early age.  Chessies are late bloomers,and often these tendencies emerge when the dog is around two years old.  Chessie enthusiasts strongly discourage taking Chesapeakes to dog parks and also recommend not to have more than one bitch in a household, as it seems bitches are more likely to become dog aggressive.
 
Chessies are also extremely territorial.  My Jasmine has jumped through my screen door to get to my gardener, luckily only to bark at him and then return to the house.  She would also sit in my bay window while I was gone to "bark at every leaf that blew past" (as my neighbor said).  I put X-Mats in my window to prevent her from sitting on the sill and disturbing the neighborhood.
 
Keep us posted with how she's doing!
 
An X-Mat
:

she does sound like a typical Chessie. Management is important for such dogs. Fix your fence so she can't get out. Keep her on leash and work on her obedience so she can't go around picking fights with other dogs. Use a muzzle if necessary. Some adult dogs don't particularly care to interact with strange dogs. That's not important; it's not a bad thing; you're unlikely to be able to ever convince her that strange dogs are fun to meet. You can however teach these dogs to IGNORE other dogs.
 
Going after cats and small dogs is often predatory behavior, and has nothing to do with aggression.

From Sandie-NY Chessie Rescue:
 
I'd do the Thyroid test, put her into a good strong obedience class and for goodness sakes, spay her. Sooner or later if she go's into Pieo, she'll have to anyway. One less thing to worry about. I'd also start giving her a very strict controlled environment and NO reward unless ask to do something and will do it. Like sit, come or lie down. Control commands. I'd never let her out side without a 6 ft leash. Ready to grab and "correct".
Frankly it sounds like to me when this first started, the dog NEVER really got a good strong correct. One that made her know with out a doubt, this was not acceptable behavior at all. Owners need to be more of a pack leader and really give her structure. And if doing this, her life style changes. If she starts to show any signs of being aggressive to her owners. Not accepting the stricter life style. Than and only then, I'd say put to sleep. Her age doesn't help her. But I do believe with "common sense" and using their head, they can manage this and she can live out her life with them. I have a couple of dogs here that would probably kill my 4 cats and kill my Cavaliers. But they've all lived together for a good 3-4 yrs. and everyones happy and intact. But it's using the common sense. Not allowing to put the dogs into a situation that can trigger this off or cause a problem. They are great with kids and people, just great. But I'd never trust them with the cats or small dogs.
I think where the problem really started is when she fully matured (around 3) and because there was really no structure or a good strong pack leader, she pushed, got away with it and now the problem is right there. Good example just why this breed is NOT for just anyone & everyone. I'm sure she's a great person and good dog owner. But takes a heck of a lot more to live with a Chessie.
Pass this on to her if you want or have her give me a call. She can get our e-mail or phone number on our web site.([linkhttp://www.nycbrrescue.org]www.nycbrrescue.org[/link]) Glad to help if she wants it.

I can't believe someone would suggest putting a dog down for dog aggressive behavior.  LOTS of people manage that particular issue just fine.

Frankly it sounds like to me when this first started, the dog NEVER really got a good strong correct.

 
strong corrections applied to aggressive dogs tend to make them more aggressive. Not a suggested course of action. Try reading "click to calm" by Emma Parsons, or "fight" by Jean Donaldson, or watching Ian Dunbars' video "Fight".

Thank you for all the tips!  The fence was fixed the day it happened, and we've been taking her out on a 5 ft leash ever since and will until we get the dog run.  I got a phone number from a neighbour today for a trainer in our area and am calling her tomorrow. 

This isn't something that happens a lot.  We are very careful with her and have been ever since she tried to attack the poodle for the first time.  We go to great lengths to keep her away from other dogs - the times she has gotten to them have all been accidents for one reason or another - we certainly don't allow it.  And when this does happen - of course we scold her!  As soon as we get her away, she walks with her head down and her tail between her legs - she knows what she's doing is wrong and she has been scolded every time.  Obviously what we were doing was not the right way and I'm going to look into the calmer ways of dealing with it as mudpuppy suggested.

I have to disagree with the suggestion that she wasn't controlled.  True, when she gets around dogs she goes into her own world - but that's the only time she isn't controlled.  In any other situation, when told, she will sit, stay,  lie down, go to the porch, give nicely (with toys or food she will only nibble to get them - she never snaps for anything), she knows so many commands and tricks that people comment on how smart she is ALL the time and say they wish they had a dog that listened as well her.  We've always spent a lot of time with her and she is very smart.  She knows I am the leader and in any other situation and in normal everyday life I could not ask for a better dog.  I don't mean to sound defensive, but it's not like she's a dog that just roams around unnoticed - she is a very big part of our lives - she's part of the family, and we've spent a lot of time training her and she is a very well behaved dog.  I know what she's doing is wrong and needs immediate attention and I am taking everyones advice - the dog run is coming, she's going to the vet, she's going to obedience school and she's getting fixed.  I want to get this problem fixed and am willing to do whatever I need to do. 

I really do appreciate everyones suggestions!!

Your girl is beautiful, always loved this breed.  Unfortunately the recourse for you before was keeping her away from dogs because of her behavior.  However, the only cure to this problem is socialization.  So please do hire the behaviorist he/she will then be able to teach you how to socialize and handle her in these difficult situations.  I bet some of it is just her feeling your tensions now, understandably.  Good luck and keep us updated.
 

Be careful which trainer you select for this dog - I advise you to heed mudpuppy's excellent advice, too!
Consistency and leadership is necessary.  But, IMO, harsh correction is ill-advised.  "Click to Calm" is a great resource, as is "Fight".  Both are written by great trainers with experience in rehabilitating aggressive dogs.