Dog growling and snapping when approached by dogs in "her space."

 Maybe your dog need to be neutered. Because  it makes your dog calmer and prevents male aggressiveness and territorial behavior.

abiannebane

prevents male aggressiveness and territorial behavior.

The OP's dog is a female.  There is some evidence that neutering males can decrease aggression but to say that it will PREVENT it is not true.  It might be part of a program to work with an aggressive dog but if the behavioral aspect isn't addressed also, neutering is usually not going to stop the behavior.

Agreed Jackie.

While it is always a good idea to alter our dogs, except in certain specific circumstances, for any number of reasons, it certainly isn't a cure all.  And I've seen that older dogs who are already agressive do NOT decrease that aggressiveness simply because they loose the "family jewels"

 Neutering may help with some dog to dog aggression situations, and spaying rarely helps with that in females.  However, if the desire to preserve her personal space is due to breed characteristics (many herding dogs do this), or is the result of undersocialization, then neutering is not the answer.  Whoever said that we used less than accurate language, and that the *potential* for aggression always exists, is quite accurate.  The problem with aggressive dogs is that as much as you try to remain under that threshold, whether it be by management, preventive strategies, training, behavior modification, or medication, the fact is that the dog is always capable, and always has weapons in its mouth.  The key is to use the strategies that make the dog better in terms of self control or obedience, but never to forget that under all the good manners you instill, there is always the possiblity of something triggering the dog.  I would say that our OP should read "Feisty Fido" and see if the descriptions in that book seem to match what her dog is doing.  If so, some great strategies for getting started in developing the dog's coping mechanisms exist within those pages.

espencer

The issue here is, aggression: always there or goes away? (regardless of the method)

You are absolutely incorrect.  The issue here is:

I've been having issues with my 50lb lab/dal mix, Alex, who is protective of her space with other dogs. I used to do dog rescue/adoptions and we had lots of smaller dogs in the house which she would play with and live with and be fine with unless she was under a chair or in a corner or in what she perceives as "her space." If approached by another dog there she will growl or show teeth. If they continue to approach or get close enough, she will snap at them. This has happened with cats too. Since we have moved into a house with a see through fenced yard she has now taken to trying to attack our neighbors dog thru the fence when it comes into our yard near the fence. She also has some fear issues (adopted from a shelter and likely previously abused.)

When we are out on walks she could care less about other dogs and even when we've been run at full speed by multiple loose dogs she stays calm and uninterested which diffuses the situation. She lives with a small dog and has several "cousins" who visit who are big dogs, and while it took her time to adjust to them she gets along fine with them now- BUT they know her quirks and her signals and don't get close when shes laying down somewhere. I understand her need to have her own space, but Im not comfortable with her growling and snapping for any reason. Even with as much as I know about dog behaviour and working with dogs, shes stumped me. I've tried every trick I know to work with her on this and have gotten nowhere. I could use some suggestions as I would like to have a zero tolerance policy for aggression with her.

I agree with spiritdogs that this dog's response is appropriate when other dogs enter her "space".  I would not correct it, but if I didn't like it that she chose that particular area to defend, then I might "set up" an area that she can HAVE (like a crate) where no one else is allowed to intrude.

I suspect that her behaviour at the fence is entirely different though.... I will be back shortly when I have had something to eat and finished reading the replies.

Edit - PS.  The capacity for aggression never goes away.  We ALL have aggression in us, humans, dogs, horses, cats.... all of us.  I know a chap who has been to anger management classes after he lost his temper with a guy and put him in hospital.  He is loads better now - but does that mean he will never slam a door, or raise his voice, or lash out - ever again?!  Of course not!  It's not that the aggression has GONE AWAY - that never happens, aggression cannot be "cured".  It's that something has been ADDED to the situation; namely a degree of self control and a coping strategy.  Should the threshold be breached, "aggression" will still be there and the dog (or person, or cat, or horse) will still react accordingly. 

Edit again - neutering is not the answer, unless the question is "What is the single, final solution to making my dog physiologically incapable of producing puppies?"  My male dog got MORE aggressive post-neuter.  With females, it rarely works and in some cases makes them worse.