I used to have a theory that when you are potty training a child you are actually training the mother to remember to take the child to the bathroom. I used this theory to potty train my first four children. It worked, obviously, but I had it wrong.
My pediatrician has a plan for potty training that is amazing. It works, even when I didn't think it would. And it sticks. Train the child when he feels like he needs to go to the bathroom. Tell him if he feels it coming to run to the potty, pull down his pants and sit down. Don't ask if he needs to go. Do tell him he needs to go. Wait for him to know. Yes, there were some wet pants the first day, but that is to be expected. That's how he knows he's feeling he has to go.
*All this being said, it took a few weeks to really get the potty thing down, meaning, it is hard to stop running as fast as this guy runs in life to have to use the potty. But, he has not had a single wet accident since the first week. We are definitely onto the next stage of life.