I have heard that you can sprinkle a little meat tenderizer powder on their food, and it will turn their poop bitter, so that it doesn't appeal to them. I have also heard that it is because they aren't getting the nutrients they need out of the food, and so the body craves poop (ewww!) to try and get the nutrients the second time around. And a way to solve that would be to change foods, or try the equivalent of vitamin supplements or something like that.