Hi, my dog Daisy who has MVD had repeated and chronic diarrhea for years due to the shunting of her liver coupled with inflammatory bowel diseases. We struggled with yogurt, flagyl drugs, and the whole kit n kaboodle for years and years. I started using a product for dogs a few years ago that takes care of the diarrhea in a flash. In fact, I just recommended it to a friend for some loose stools in her household! I swear, this is easier than the yogurt. Keep it in the fridge, it's great to have on had for the doggies.
Good luck. Here is the link to the product we use and love from the online store we order from (they are a little slow to ship though!)
Acidophilus for Dogs & Puppies, Dog Probiotic, Kosher & Lactose Free - 16 fl. oz. - Dynamic Health