Pajama Help

Ok mommies, I need some help. My son (11 months) has figured out how to remove his diaper. It has resulted in finding him naked when put down without any pants on. I thought we would be fine with pants, but was proven wrong this morning when my husband went in to find him bottomless and covered in poop as well as having eaten some... I prefer the 2 piece pj sets since they grow with him better and they're easier to change his diaper in but it's looking like I'm going to have to switch him back to 1 pieces. Unless anyone has any other way I can get him to keep his pants on?