K.
I tried EVERYTHING with my almost 3 year old and I KNEW that he was capable so finally I brought discipline into the picture. I explained to him that I knew he was a big boy and knew how to use the potty so everytime he went in his pants without telling me he needed to go and at least finishing on the potty he would have to stand in the corner. I KNOW it sounds horrible but he was back on track in 2 days and no issues since. I think it's the same concept as giving in to a tantrum - once a child realizes an action produces a certain reaction or lack thereof they think it's okay. This could have simply started with him being too "busy" to want to stop and go poop but because there was no consequence why not keep it that way? As parents when we are surprised by a new behavior we don't usually react because we aren't sure of the why. My daughter cry's when she goes to bed about once evry 6 months and because it has been so long since it happened I run right in to see what's wrong. This sends a message that if she cry's I'll come in and we do this for about 4/5 days until I stop going in and then she stops for another 6 months. The first intitial cry may have been legitimate but after that it was for my reaction. The first intitial time he pooped in his pants may have been legit but now it's because there is no consequence so why not? I wouldn't reccomend a pull up because I think that sends the message that it's okay and it's NOT. At 3 years he's old enough to understand action and consequence so a few minutes in the corner won't hurt him and if you keep reminding him that he's there because it's not okay to poop in his pants he'll stop
Also my Pediatrician recommended making him clean himself up because he was the one who made the mess. This might have worked if I could handle having the poop everywhere but I couldn't.
GOOD LUCK - I KNOW it's frustrating!!!!!!!! :)