I would get a trainer involved. Personally, I will not go to dog parks and I would never schedule a play date for my dog. I exercise him. We go to dog club once a week. Those dogs all have responsible owners and there is never a problem that blows out of control.
Before a fight happens there are signs. When dogs are together they have to be supervised at all times. Not just being present, like actually paying attention to the dogs. My oldest dog just barely will raise one side of his lip showing his teeth. That was enough to start barking, then growling and sometimes a fight. It was so slight I missed it the first few times. I was wondering why the GSD was always getting in the oldest dogs face...well the older dog was being a turd. That has stopped!
Riley - 11/05/2012-8/30/2013 (Myasthenia Gravis)
He will always be in my heart.