I didn't read the posts, but here is my opinion on dog parks.

I use to love them, and take Josie there all the time. However, the exact same thing you are talking about Bon happened to Jo. One day she just decided she didn't like the way some dog 'looked' at her I guess, cause she growled at him. She's been dog aggressive ever since. I've talked to a few trainers, and they both tell me they get a lot of people who's dogs become dog aggressive from being at the dog park. I won't take my dogs there anymore, or to any dog park unless it's for a PT meeting...

Josie doesn't mind SOME dogs, but she will attack other dogs. She growls at them and just hates them. She was always VERY good around dogs. I duno, maybe think about going back next time? Is there somewhere else he could run?? I'm no dog expert, but this is just from my experience and what others told me

I guess some dogs just aren't that nice. Perhaps they do something to other dogs that angers them? I have no idea.