What an interesting thread.
We don't have dog parks over here but even if we did, I wouldn't go.
I'm very, very careful when I am out and about with Hogan. If I see a dog in the distance Hogan is on a lead until we either have passed them, or we have met them, and I am sure they are friendly. Recall is good, but he is only 5 months, and will run straight up to a strange dog if I allowed.
This method failed me a few weeks back when a strange dog ran up to us and attacked Hogan. The owner was arrogant and didn't care. I reported him to the dog warden, with pictures, but nothing has come of it, which is disgusting.
Luckily, Hogan is a happy chappy, he has met many dogs since and is perfectly fine. He wants to be friends with everybody.
I worked very hard to socialise him properly and hate the fact that irresponsible owners don't bother and the others have to suffer!