T.F.
Hi M.,
My son will be 4 in December, and I started potty training him at 2. I had the same problem. He knew how, just didn't want to stop playing to go. I tried everything and thought he would never be fully potty trained.
I kept telling him you have to go potty when you wake up or even while you are watching T.V. because that's what big boys do. That's what daddy/grandpa/boys at school do, and you have to too since you are a big boy. And I think it finally started sinking in. It wasn't an immediate fix, I'm sorry I don't have one of those for you, but don't give up. Your son sounds like mine....they do it once and know they can do it, then don't do it again until they are ready to do it permanently :)