There can be several causes of stool eating (also known as Copropagia) in dogs.
Terriers fed diets they can't properly digest will eat their stool because they consider it semidigested food rather than waste. Dogs will also eat the stool of other animals whose waste displays similarly appealing characteristics.
A change in diet will possibly solve this problem.
Owners can become obsessed with a dog's stool (due to a medical problem or when the owner takes a heavy handed, highly emotional approach to housebreaking). Your terrier may eat the stool to avoid dealing with your response to it.
It's best to put your emotions on hold and seek to identify and eliminate the real cause of the behavior rather than merely eliminate the behavior itself.