I have a number of hollow plugs, the issue I found with using them to romove the ability to stop pooping is the fact that if the plug is small enough to fit in (comfortably) then when you need to poop and naturally push the poop out then the plug always comes out first. They can be used in conjunction with an enema, but that comes out pretty instantly! Which makes diapering difficult. The only plug I have that doesn't come out easily us so big that I can barely get it in, and certainly couldn't wear it long term. I'd be interested to see your design. I would suggest that it needs a very flared base with a very flat bottom to make pushing the plug out harder.