Did you know that off leash, enclosed dog parks are very dangerous places for your dog? I am not really a fan.
When you have a number of dogs running together they will form a pack or hierarchy. If a number of those dogs go to the same park often, they will also regard that park as their territory. This can be a recipe for disaster. A newcomer coming into the park can be seen as an intruder and can easily become a victim of a dog attack.
I personally think that all dogs that enter and are allowed to run free in a dog park should be shown to be completely under control by their owners. Their recall should be reliable, so that at any hint of trouble all dogs can be called back by their owners immediately.
The reverse of this is actually true, with many owners of untrained dogs visiting these parks because they want to let their dogs have a run in an enclosed area, where they won't lose them. If a fight was to break out not many owners would be able to call their dogs back to them. Definitely a very dangerous place for your dog to be.