I just saw this and I had to respond!!! My daughter,2 1/2, is currently Potty Training...and really...one day she thought that it would be fun I guess to go in the potty! She also runs naked everywhere. We went through the fits over the undies as well, and that has since passed! I even bought her boys underware with race cars on them. This week we have had 2 big breakthroughs!!! Sunday, we were out shopping for like 3-4 hrs., and had NO accidents, and she went on the 'big potty' at the stores, and then today she finally pooped on the potty! This really is a thing that will eventually just kinda come to them! I know that this sounds like I'm rubbing it in...but I'm not, I promise! And we don't have nap or bed time even thought of yet, but when she's up, the undies are on...and we use the potty!!! I really think that he will come around, and just do it one of these days, and shock you!!! or, if very concerned, call his doctor! Maybe they will have some different advice for you!! Good luck and take care! -C.