R.S.
Mine did that until I made him clean himself completely with as little help from me as possible. I would hand him wipes and hold the plastic trash bag. But he had to take off the clothes (in the bath tub, easy to control and clorox later), he had to wipe himself clean and then take a quick shower (in water slightly colder than his normal comfortable temperature (NOT a cold shower, just not his ideal temperature).
He only had one accident after the first time...so once he knew he was in charge of cleaning up the mess...it stopped.