try swimming him (hydrotherapy) helps heal injurys, i worked in a hydrotherapy centre (dog swimming pool) for a while and i tell you it works wonders on injurys to joints as it builds up muscle but without putting weight on the joint....i was sceptical on the whole "it works miracles thing" till i saw it before my eyes, although at £30 for half an hour its a bit pricey, personally i would go for the swim him up and down off a jetty option as its free