Random aggression on leash towards other dogs

If I were you, I would avoid other dogs for now.  When you see another dog while on a walk, turn around or go to the opposite side of the street.  Or you can make him sit stay on the side until the other dog passes.

I think he might be doing this because he feels the need to protect you.  I'm not a big expert, so I'll wait till someone else gives you better advice.

I haul him off, grab his muzzle and tell him no barking. The bark seems to be getting worse and more menacing.

 
You are inadvertantly making the situation worse!!!!  Stop grabbing him and scolding.  Please get a copy of "Scaredy Dog" by Ali Brown.  It will help you re-think your training efforts with this dog, who just wants to be social.  If you continue what you are doing, you will end up with a dog you can't take anywhere...
The fact that he is good off leash tells me this is not aggression, it's reactivity.  And, that is a situation made worse by the handler, so you need to learn how to deal with it without contributing to the problem. 

I am also one who deals with this issue with a cavalier spaniel. I try at all cost to avoid other dogs when i see them coming with their owner. Its hard to avoid them because this area is loaded with dog lovers. I cross on the other side of the street way before the other dog is near but my dog growls terribly and lunges practically pulling my arm off/ The other dogs pay him no mind and i feel like I have a maniac. He is in his own zone and no amount of treats or calm behavior on my end helps. I've spent money on training and keep telling my self it will improve, its been 9 months and nothing has changed. Its very exhasting taking hiim for walks and I feel bad but don't know what else to do.

My dog is also leash-aggressive (well, dog aggressive in general save for a few she knows)

This helped me very much -->

When a dog approaches, I give Ginnys leash a light snap to her her attention, and tell her to sit. You may be thinking "No way will my dog sit when he sees another dog! I can't get him to focus!" But actually, it is, with most dogs, very easy because they respond "automatically"  when they are focused on something else.

I use the sit as a "tune-down" position. That is, Ginny knows she is sitting and to hold the sit, so she relaxes a little because she has something else to think about besides "OHMYGODDOGDOGDOGBARKBARKBARKDOGDOG!!!"

I would try to find something that gets your dog's attention away from the other dogs. Make him sit and offer a treat, or a squeaky toy, etc.  He will eventually associate an approaching dog with a) paying attention to you, because you will be giving a command, and b) a reward. Not just an opportunity to go nuts Good luck

If your dog still lunges, do not yell, etc. One firm NO, and a stern look, and a repeated "Sit" is enough. Too much discipline will only heighten the tension of the situation and make it worse. Before I figured out that Ginny would behave if she was sitting, I would drag her off, yell, etc when we passed another dog, which would only frighten her, or increase her anxiety, and cause more problems. Focus on creating a controlled environment.

He is in his own zone and no amount of treats or calm behavior on my end helps.

 
What this usually means is that you have simply allowed the other dog to get too close before starting to get your dog's attention focused back on you.  Some dogs have a very long "critical distance".
 
Have you read "Click to Calm"? 
 

When a dog approaches, I give Ginnys leash a light snap to her her attention, and tell her to sit.

 
I'm glad this worked for you, but it is contrary to the advice we usually give.  If the dog is fearful, a leash yank can mean "oh, gosh, my human is afraid, too, so no one is going to protect me - bark, bark, lunge" or it can mean "darn, I hate other dogs, my neck always hurts when I see another dog".  This is why handlers who snap the leash often make the situation worse. 

spiritdogs - oh no, I definitely know that - I don't "snap" really, only give it a very light tug, just to get her attention (this is just attached to a halter, not a choke chain or even a collar).

I've just decided that each dog is different, just like children. and what normally works with most dogs just doesn't work for mine. Because I adopted him and don't have any history on him I don't know what he may have encountered before me. I am at my last hope with my Buster. I am going to try averting his attention with a treat that he loves. It may be bribing him but I am willing to try just about anything. He practially has me walking back home in tears because he is just so focused in his own zone when he sees other dogs that no one can get through to him. I end up dragging him up the street even when the other dog is almost out of sight. It becomes heartbreaking when you hear comments being made about your dog from passersby when you know you've really tried..I love this dog and have had him 8 months now, but it is wearing me out trying to walk him.

I have to chime in here! My situation is ahem, smaller - but pretty similar. See, I have a 5lb chihuahua. He is a little over a year and a half. Obedience, daycare, other dogs, the works - and then he developed the leash aggression. My walks with him were like yours: I absolutely felt like crying after he'd go bonkers on the leash. I was one of those people you roll your eyes at and go, "Another chihuahua with a Napoleon complex"... Sometimes people would laugh because he was a small dog 'acting tough' but it broke my heart because I knew it was a small dog who had become fearful and aggressive, for whatever reason. Here I was, like you - apologizing to the other owners, avoiding other dogs and dreading our daily walk. (thanks to spiritdogs for diferentiating the aggression vs reactivity..that is so interesting to me). However, you don't have the luxury of physically picking your dog up...which I can appreciate makes it that much harder.

So, I got to work. For a little over a month I have been working daily with him (he is also dominant in the home, so we worked on this @ the same time). Here is what worked for me.

The Gentle Leader. I had a dog trainer come to the home and show me how to use it properly. We went for a walk (where we saw a dog) and she showed me what to do.

The "Watch Me" command: for distracting him BEFORE he had time to react to the trigger.
Saying it, then rewarding with a treat.

After the Gentle Leader, I switched to an Easy-Walk No Pull Harness. Which still allows me to physically divert his attention to me. I have been working on having him walk nicely on a loose leash and heeling. He is never allowed to walk ahead of me.

I always give him a wide berth around other dogs. It took a long time before we could pass a dog on the opposite sidewalk. But now - we can. And just today my boyfriend walked him PAST 2 dogs on the same sidewalk. All he needed was a gentle correction on the leash to distract him out of a possible barking fit and he kept going, bark-free!

Now that I see it's actually working - I want to KEEP working with him.

I was wondering - is there a dog-free place where you can run your dog first before you do any leash work with him? If he is tired, he might be more relaxed on your walk and therefore less reactive.

I know we still have a lot of work to do. One thing I read (I think it was in Cesar Milan's book) that I recall whenever we have a bad walking experience is that long after the negative incident has occurred, the human is still stressed out about it. But your dog lets it go right after it happens. Your dog doesn't go out with you, worrying and planning to bark at other dogs. So, try to let it go - just like he does. And make each new walk a new possibility. Go into it with confidence, not worry - even if you have to fake it at first!!

Good luck!

Loki and Odin have been I guess reactive, instead of leash aggressive, also. I've worked on it for a while (mainly just keeping myself calm when we pas other dogs, so they don't feed off of my nervousness) and they are much better. They still pull and bark just a little, but it comes off much more excited/playful than it used to.
 
But I still have two problems. The first is that walking two dogs makes it much harder to have them both sit and focus on me when another dogs passes and I really don't want to have to walk them seperately. And the other problem comes when you encounter someone else trying to have their dog sit and calm down.Then you've got two groups staring at each other and no one walking. I don't know what to do in that situation. Anyway, since we were on this topic, I just thought I'd add that in.

Why don't you want to walk them separately? I really don't like walking mine together. I like having better control over ONE dog and can't focus on training one, when they are both trying to grab the training treats! Only one of my dogs has leash aggression. I don't want the other one to possibly pick up on his bad habits.
 
I think you need to work with your dogs' individual comfort level. If you train them separately, you might find that ONE of them can handle a closer distance to other dogs, while the other may not.  If you have them together, and ONE decides to get antsy, the OTHER could  feed off of that.
 
As for the sitting when other dogs pass -what if you just try crossing the street long before the other dog gets to you.  Having another dog walk past your sitting dog could be infringing on his comfort zone @ this point.  When I see a dog headed our way sometimes, I turn around OR cross the street OR get up on a lawn to give that dog a wide berth.  And THIS is when I do the distraction training. Eventually we have been able to work up to closer and closer distances with less stress.
 
If you want to try the sit thing, I'd recommend a Gentle Leader. You can direct the dog's head to your face, so he physically cannot look at the passing dog.
While all the time feeding him the best treats ever! I did this with a chihuahua - so it can be done. But I'd get a trainer to show you how to use it correctly first.
 
And if you encounter, someone else with a sitting dog, I'd just cross the street.
No point in having a stare-off. This will agitate BOTH dogs! Good luck!
 
 
 

Well we walk 3-4 miles every day, so I just don't want to do that with two dogs. They walk great together and I think walking together bonds us all (Odin has only been with us a few months). And crossing to the other side of the street is not really an option where we live. We walk either on 10 foot wide trails (there are about 10 miles of trails behind our house) or along a 4 lane divided street with a huge barrier in the middle. So getting away from another dog is not an option. I know that I should train them seperately to work on sitting and focusing on me, but like I said my overall goal is to walk them together.

gnatflea --Thanks for your response. I need to learn how to not let other dogowners comments get to me and just have a bit more patience. I've dealt with him for 8 months and I love him terribly. Sometimes it just helps knowing that there are others out there like myself who are dealing  (or have dealt) with these same issues and can lend a supportive ear. I have also started walking them separately, more so in the evenings because I have more time to do double duty. The mornings are a bit more short on time.

I can't believe that it was almost 7 years ago when i wrote this original post. I am happy to say that I stood by Buster for all these years and now I can happily say that this year 2013 Buster has finally realized (or gotten to old to care) that other dogs are no threat to him and he doesn't have to be aggressive. We now go for our walks and unless the other dog barks at him first he really doesn't care. And even if he does bark back I tell him "No' and he continues on with his sniffing the grass which he spends most of our walktime doing. Patience is long suffering, but Buster was worth it.