My dog has a bad gut - any ideas?

Try giving him Canine Gastralox. It is specifically made for dogs with vomiting, diarrhea, ulcers, and food/water avoidance. The Canine Gastralox will coat the his tummy and digestive system, neutralize whatever acid or other stuff is in him making him feel bad, and restores the damaged lining. I think they have free samples on their facebook page or if you go to gastralox.com.