Dog parks - great places but there can be lots of issues between dogs and also between humans in dog parks!
One of my ex clients has a beautiful little boy, a Westie, and he has been classified as menacing because there was a scuffle in a dog park and him along with a few other dogs 'ganged up' on another dog and now the council is involved.
What owners have to realise is that dogs will be dogs, dogs do this type of thing, what owners have to do is MANAGE their dog as best as they can. If their dog can't be in a dog park situation, then manage it and don't take the dog to those places. Instead, either take them elsewhere to play and run around or simply take them out walking or running instead...play ball in another park, play tug of war, teach them or practise obedience.
Not all dogs will get on with all dogs......just like us humans, not all humans get on together either!
You dont have a bad dog just because he/she wont do well in a dog park.