Why does my dog poop in his food dish:o

I think it is claiming it. I once had a dog that would urinate on his when other dogs were around. Many books are more likely to suggest it would never happen than explain why or what to do about it.

My latest puppy training manual has a procedure to use with dogs that are aggressive around their food dish. Maybe it would help you. Start with only part of the dog's food. When it is finished, take up the dish and add more. The dog should quickly start to welcome your attention to its dish.