C.J.
I had the same problem with my daughter. I had her fully pee potty trained in 3 days, but poop for some reason was really hard. It took about 2 months to finally get her to go in the toliet. I tried rewards, sticker, toys, taking away previlages, having her clean up her own mess (which is nasty) and nothing worked. She loves Go Deigo Go so I went out bought a bunch of boy's underwear came home and told her that Deigo and baby Jaguar would be very upset if she poops on them. It worked she started pooping in the toliet and we never had anymore problems. It is worth a try. Best of luck I know how fustrating this can be, but he will get it.