How is your dog’s weight?
Keeping him active is important. You can try adding a glucosamine complex to his diet (Glucosamine, Chondroitin, MSM, Vitamin C, etc) There are quite a few options available. I give my dogs Nupro (and they love it).
Have you tried a raw diet? That might also help. You can also look at natural foods that have anti-inflammatory properties (celery, tumeric, etc.)