Stool eating can be caused by 2 things....

1) a deficiency in a digestive enzyme. Take a fresh stool sample to your vet and ask for a 'film digestion test' to check for a deficiency in the digesting enzymes. If there is a deficiency the treatment is a inexpensive pill at each meal.

2) a bad habit.

I'm unaware of anything else that causes that problem.

Keep the stools picked up right away and check the stool sample with your vet to rule out medical problems.