What can I do to stop my dog's aggression towards intact dogs?

At the local dog park, our dog (a boxer/GSD mix) interacts well with almost all other dogs, but every time an intact dog enters the park (against the rules, I might add), he growls and acts aggressively toward the un-neutered dog. Is there anything I can do to correct this behavior?

its a donamint thing the neutered dog is giving off singnal saying its better and will try to be better and so your dog might get mad and try to show whos boss

Why are they coming into the park with an intact dog? I may not be correct...but I think it is fear aggression. He knows that the intact dog wants to be dominiant, I think...not too sure though, sorry...Good luck though!

You can contact your local animal control agency, or your parks district and report the rule breaking. But know that you're breaking the rule too by having an aggressive dog in the park [even though its triggered by in-tact dogs], so be careful. The best thing I can tell you to do is to watch the dogs coming into the park, when you see an in-tact dog, leash yours, walk to the person, and inform them of the rules.Sure, you may look a little silly or over reactive, but you're keeping your pet, their pet, and the dogs in the park safe.