My bridge girl could not go to a dog park since she was other dog aggressive.
When I first adopted Deniro I took him to the new park here. Deniro has NO prey drive what so ever. He was fine at first until a very hyper standard schnauzer decided to hop around him and get in his face. Deniro tried to warn him a few times and when the owner of the schnauzer did nothing and the dog didnt quite understand the warnings, it was on. Deniro went after him to tell him quite effectively to BACK OFF. At that point I was not going to risk it and we left. Have only been back when it was empty on one side.
I have taken the boys to play group at our kennel a couple of times. Greys only and all muzzled. Both boys loved it.
But once a week we go to the kennel anyway and the boys can run alone in one of the pens (about 1/4 acre maybe larger). Other times I can take them to my mom's since she has a large flat fenced back yard.
Both boys sniff, sniff, pee, sniff, sniff, poop, sniff, sniff, pee some more and sniff some more. Then Deniro will try his best to get Bernard to play. Eventually they will run all out. Then they are done.