Our dogs also tend to be pit mixes, so you may definitely have a point. Another thing I consider is that living at the shelter itself could contribute. Of course the dogs are housed separately, and at ours, we have solid walls between them, but still they are hearing, smelling and seeing the other dogs, with the barrier between, which could be frustrating. From our own personal experience with our own dogs, though, I still really believe that dog parks strongly contributed to their issues. However, I am sure a lot of it was our reaction to events at the dog park, as well as our lack of experience and knowledge when we started taking them there.