S.G.
Put him in underwear and just get rid of the diapers. It will be messy for a few days but just do it. Also, make him wipe himself if he goes in his pants. Make potty trips easy but if he is wet or dirty, make sure it takes a long time away from whatever fun he was doing. Reward! Reward! Reward! Whatever it is that motivates him. At this age, I would do a small reward after each time. With my son, he has trouble with BM but we had a bunch of hot wheels cars so he got one after every poop in the potty. Never had an accident after the few 2 times. He was just over 2 so a long term reward was not going to work. HTH. S.