That is a hard one. Did you adopt him from a shelter or rescue area? Did he come from a breeder? My husband and I started feeding our dog food that the shelter normally feeds him (as well as giving lots of nutritional treats for training times)–Purina One (Adult). Many of the ingredients listed (at least top 5) were decent–a meat was number one, need something with fat, grains/rice, etc… He had no problems with these, but when he got sick after getting into something that didn’t sit well with him, we got a few cans of moist food to help regulate his tummy. Natural Balance is a great food that uses all natural ingredients–our dog trainer recommended it. After our first bag of Purina One, we decided it might be nice to try something else, to see if food was the reason he has kept biting at his tail, chewing on a few spots on his legs (he seems to have dry skin in these areas). We are now transitioning him to Eukanuba, and that has always had a decent reputation–have never heard anything bad.
Has your dog ever been tested for allergies? I know if a dog has certain allergies to ingredients–chicken, rice, fish, etc.–that could be a cause of why he’s not eating? I have no idea how animals are tested for allergies, but it could be something to look into.
Other than that, maybe doing a mix of moist and dry. Some dogs will only eat like that; some only kibble, some only organic stuff–guess they can be just like humans who are picky eaters. 😛