sometimes loose stools can be a result of a food allergy/sensitivity.
i have know of a few dogs whose stools firmed up when they were fed a different brand/type of food.
my Pitty was very sensitive to corn and wheat, once on a dog food without either ingredient.....no more problems!
There is a herb called Slippery Elm Bark powder that is one of the best herbs for treating any digestive disorder....google it and check it out. it is very safe and effective.