My town has what they call a dog park. It is less then a 1/4 acre, may even be 1/8. It has crushed rock(ouch) for footing. I have only used it when no one else was there, using it for a fenced in area so I could safely do off leash obedience work in a strange place. I leave whenever anyone comes in. I have watched the dogs and owners and I don't like what I see. I do know that groups of people make "play dates". In that case all of the dogs know each other- same with the owners, but even then there are problems. The reason I know this is that I go tracking in the fields adjacent to the dog park.
I used to take my two older dogs to a very large(100 acre) dog park. The first two times we had a very good experience. The third time, my young intact male wanted and tried to hump a neutered male. I had to keep dragging Duncan off of this poor dog. I never did see the owners(you would think they would come running if a rottweiler was mounting their dog- at least screaming- I would:D ) The 4th time, we were leaving and had the dogs leashed up. A guy with his very ugly rottweiler was coming towards us. Before I could warn my husband, the ugly rott attacked Duncan. Duncan needed vet care. After I got the other dog off, the owner took him and instead of leaving or even appologizing, he kept on going into the park. I now wonder if he was using his dog for fighting.
My dogs only play with dogs that I know. I expect my dogs to behave around other dogs, to ignore other dogs when under my control. I strongly feel that dogs do not need to meet other dogs on the street or parking lots. My dogs have been attacked, and it is ALWAYS the rottweiler's fault, forget the fact the rottweiler is the one leashed and the only wounds are on the rottweiler.
If you are always with the same people/dogs and they all get along, then fine. But if a strange dog(s) enter the park- the pack dynamics change and there could be problems. I am just tired of taking my dog to the vet. I also had to stop showing Duncan for more then 6 months because of that attack- he was afraid of other dogs, it took professional trainers to get his confidence back- to the tune of $600.