The main problem is that the size of the dog park makes it impossible to get to him in time. It's like he's on the lookout for dogs outside the park. That and he's quite evasive and you just end up looking like a right goose when you try to catch him. I understand where' you're coming from with the obedience training. Unfortunately, being a rescued/pound dog, he didn't receive any training at all and now that he's 3 years old, he's quite set in his ways.