I do not take my dogs to dog parks only for the fear of them getting sick or injured by other dogs. Dog parks although are a great option for some people. With an unaltered female it does seem like risky business in the case of an unaltered male. Your dog might not even enjoy the dog park visits because of other dogs' behaviors (even though I think that other owners should better control their dogs). It sounds like the owners at this dog park are pretty laid back (which is expected of dog park dog owners, and isn't always a bad thing). I hope that one day your dog can happily frolic at dog parks, but for now it might not be the best idea...hope everything works out!