If your boy is vomiting with the Metacam, it should really be stopped. NSAIDs (which drugs like Metacam and Rimadyl are classed under) can cause gastrointestinal disturbances in some dogs, this occured in my elderly arthritic Lab as well. There are alternatives that can be used though-my dog is now on Catrophen injections and he is doing well on these.

How long ago did your dog start the Metacam? Another alternative that can be used with prescription medication is something like a good quality glucosamine/chondroitin. This helps build cartilage tissue and in moderate arthritis it can really be of benefit, where medication is concerned occasionally the dose can be lowered if the joint/cartilage is improving. Hydrotherapy would be worth a try if a) he likes swimming and b) the pool therapists are trained in medical therapy programmes. The pool should contact your vet for a referral so they can work on the most beneficial programme but generally this can help arthritic dogs (and even cats!) very well.

Best of luck.