Me too.
I don't recall if you were home cooking for your dog, but, knowing what he or she is eating goes a long way. One of my dogs suffers from a form of juvenile arthritis. Keeping his weight down, and providing gentle exercise helps to keep joints functioning. Since your baby is a Lab, swimming would be ideal, it is the #1 exercise recommended for arthritic dogs. Eli takes In Clover K9 Connectin,, and is doing quite well. I am not familiar with the ONP Arthritis Kit, but I am sure it is top notch, as all their products are.
As for the urinary incontinence, that will happen to us all as we age. Perhaps the use of an "under garment" would be the best bet, along with the supplement you already use. Supplements take quite some time to notice an improvement, so, don't be discouraged.
We wish you all the best!