If coming back when you call always ends in going home, who can blame him? :) So you need to associate recall with something good instead of 'end of fun.' Can you practice recall in the back yard? Calling him several times before you return to the house and rewarding him with high value treats. After a week or so of this, when you do go to the dog park, call him back immediately and reward. Then call him back periodically, give him some pets 'good boy' and release. He won't know when the session is over if something good happens most of the time. Recall is a potential lifesaver for your dog, so it needs to be solid and reliable even if you never take him to the dog park again.

I don't just use recall at the end of our romp, I use at home and throughout our hikes and reward accordingly. No, the real problem is that he associates walking towards the parking lot with going home...and no verbal command or yummy treat works at that point. I've tried heading in the opposite direction to make him think that we're going to start our hike all over again, but he is much too smart for that, so that trick doesn't work too well. I think he needs a training tune-up. I took him to the dog park today and he did very well with recall, so I have hope. :o)