I truly believe that the only way to successfully potty train to is get rid of the diapers/pull ups, etc. Doing dry checks and giving 1 m&m for each successful dry check worked for us. I gave 2 m&m's for going potty on the toilet. The other thing that I would highly recommend is reminding him to go potty and pay very close attention for a week, don't let him out of your site until he has his first potty of the day, and take him to the potty or at least ask him if he has to go, every 45 min to an hour after the first potty. You can be real aggressive for the first day or two and just pump him full of fluids(I mean give him whatever he likes-pop, juice, choc milk, anything to get that bladder full) for the first 2 hours of the first day and he will have to pee a lot. Take him every 20 mins or so, he will really have to go a lot and it will help him remember what it feels like when he needs to go, so that he can be more aware of the signals his body is giving him.
Mine did great for a week or two, then would relapse for several days, then do great for a few days then have a bad spell. When she was tired or super busy, she had accidents. TAKE away the diapers, play in the room without carpet, or stay with him most all of the day (postpone the housecleaning, etc, grab a book and slow down for a week or two). The house will be cleaner anyway, without the accidents.