Just a word of advice when giving any of these med's to an older dog...always investigate the possible side-effects. My last German Shepherd began taking med's (Met-Cam) for his arthritis and it (literally) blew his stomach out. He'd always had a very sensitive tummy and I was aware of the risks, so it's not my Vet's fault. We got 2 good weeks out of him in the end, which was better than watching him try and climb the stairs. I miss you Kody...
With any pain medication (especially the NSAIDS or non-steroidal anti-inflammatories), there can be side-effects and some of them can be quite serious. If you read the insert on Rimadyl, it says that the medication can cause death.
HOWEVER, I still consider most of these NSAIDS, especially Rimadyl, to be quite safe and very effective. To minimize the chance of side effects, we recommend a full blood panel prior to starting the medication. We repeat the bloodwork every six months if the pet is still taking it.