ok guys, i get it, i am a dog. i know we're always hungry and if food is available we want to eat it. that does not mean we should be overfed! now i don't really like talking about bowel movements (although mine happen to be nice, small, and smell-free) but overfeeding is a reason that causes diarrhea!
lucky for you i will share a secret that should be well-known. you can eat plain canned pumpkin to help firm your stool back up. half a teaspoon for dogs weighing up to 30lb, one teaspoon for dogs between 30-60lb, and two teaspoons to one tablespoon for big guys!
be sure not to give too much though...or you may get the opposite result!
now go tell everyone about this! save time and money and stay away from the "prescription" canned food your vet will give. however, your human needs to make the call depending on your stool (how long it has been runny, or perhaps if there is blood in it) if veterinary assistance is needed.