It sounds like your boy may have arthritis. You could try some tablets to help him with the pain and mobility from the vet.
You could also try gently giving his back hips a light massage which again could help with mobility and pain (gentle massage as the area could be tender). Aromatherapy can help.
Personally I would try these things before considering anything else. As long as he seems happy and has some quality in his life it's all good. Older dogs often have mishaps and I personally wouldnt worry about this part. Once he is not liking his life any more then please love him enough to let him go. It's the hardest part of loving an animal (I know). Now I need to go and have a little cry. good luck.