Agree with all above. Assuming vet has ruled out colitis, pancreatitis, swallowed objects, parasites etc, it may be a simple cure with diet. Try the bland diet of boiled turkey and rice or egg noodles for a few days and see if diarrhea gets better. If so, try switching to a low allergy grain free non chicken kibble like Acana duck and pear, Zignature venison, or better yet to a limited ingredient dehydrated raw like Honest Kitchen Spruce. You can also firm up stools with 1 tsp per day of soaked chia seeds, or 1 tablespoon a day of canned pumpkin ( not the pie filling one ) since chia seeds and pumpkin are good for both constipation and diarrhea; or 1 tsp a day of food grade diatomaceous earth. Also add some probiotic eg. a doggy probiotic such as Proviable DC, or live sauerkraut from refrigerator section of health food store.