My 12 years old Golden also has arthritis. I give her Synovi MSM, which has glucosamine and Vitamin C plus organic flax seed oil to lubricate her joints.
We've tried every other antinflamatory drug before Rimadyl (they all may have side effects) and nothing worked. Now she's taking Rimadyl and doing much better. If you can have your vet do liver function tests every couple of months then you'll know how your pup is reacting to the medication. In my case, after trying everything else, I decided that giving her Rimadyl was better than seeing her in pain. So far all her blood tests have been fine.