This is very, very normal and he will eventually get over it. I would let him continue doing it in the diaper, only give him an option. Maybe as part of your bed time routine, or even earlier in the day if it works better, tell him to let you know when he needs to poop and you'll help him get a diaper on, and that you'll change him when he's done. If there's no battle to fight, the thrill of the fight will be gone. Once you get past the battle part, start asking hime if he'd like to try the potty or stick with the diaper. Be very non-chalant about it, and don't say anything negative about using the diaper instead of the potty. As far as rewards, there can be an immediate reward system (stickers, M&Ms, etc.) or delayed reward. Delayed reward might look something like this: go to the store without him and get something awesome for the reward. Something with a lot of parts will be best. Maybe a train set with lots of pieces of track and several engines/cars. Put the box somewhere visible -- on top of the fridge, a bookshelf, entertainment center, etc. Don't say a word until he notices it. When he asks about it, leave it up there and stand with him while you gaze at it in awe. Agree with him that it's great, and tell him that when he's "ready", it can be his. He may say he's ready, or he may throw a fit for it, or (if you're lucky) he may ask if he's ready. Make sure he knows that "being ready" is the goal. You might ask him if he'd like to know what needs to happen for him to be "ready." You can tell him that you'll know he's ready when he's "done with diapers." Ask if he knows what Done With Diapers means, let him know that it's when he chooses to poop in the potty and not a diaper. And, rather than give him the whole thing at once, maybe every time he goes in the potty he can get a piece of the track.