@fBoyle-- My dog had the same issue. I mentioned it to my vet and he told me to giver her milk with water in it. I mix water and milk at a 1:1 ratio. She doesn't get diarrhea anymore, you should try that.
If your dog likes plain yogurt, or egg whites, you could give him those as a daily snack as well. The good part about yogurt is that it contains beneficial bacteria so it regulates the digestive system. If your dog regularly has diarrhea or constipation, yogurt will help a lot.
Especially pups need to be given a lot of calcium rich foods since their bones are still developing. Calcium deficiency in dogs can be detrimental when they are older as they can easily suffer from fractures and osteoporosis.