Pull-Ups or some other "mess catchers" have to be worn! Hopefully something thin enough that cant be noticed by others so that he will not feel embarassed at all. He cannot be made to feel bad about this!!! But yet he will mabey be aware of the "underpants" enough to remind him to not poop.
A doctor visit physical check of the colon anus and sphinxter muscle, and other areas. Mabey even the neurological signal that helps one to hold it in, is troubled? Things such as that.
I once had some major fatigue and thyroid problems and after my doctor asked about my diet, she mentioned the possibility that I wasnt getting any iodine! (I had just switched to un-iodized sea salt or something stupid) So I bought the old Mortons brand and have not had a problem since! I don't know if thats what fixed me, but it could have, and it was very suspiciouse timing. Praise the Lord!
Then great counseling from a loving church source or psychologist. And, there HAS TO BE a website that has info/support/stories from other parents and children who have dealt with THIS SPECIFIC ISSUE also! Google your heart out!