Have you tried adding a little chicken to the dog food. I have one very picky eater, and if i don't add some chicken I cook up, he doesn't want the dog food.
You can also mix in some ground beef--just a small amount--then some warm water, then mix in dry food. No snacks or treats during the day, and NO people food. See how that works.
I didn't have think this! My veterinary has said that Gipsy was in good health (apart an otitis on which I treat), but that's true that her food is hard! Now she sorts out its food, she leaves all square!