Firstly you could start him on
Glucosamine and Chondroitin supplement. It really does help. You hear that the dog has to have taken it for a few weeks for there to be any noticeable change, but I have found it can take effect quicker than that.
To give you an idea of dosage, my dog weighs 28lbs and I give her 500mg Glucosamine, and 200mg Chondroitin daily. If his weight is twice hers, or approximately, you can give double that dose.