Hi there - I'm sorry to hear that your buddy is starting to lose control of his faculties.
It's not uncommon for older pets to begin to lose their house training and "forget" that they need to go outside to go to the bathroom. It can be a combination of senility, forgetfulness or actual loss of their house training. Sometimes, in the case of laziness on the pet's part, you can improve the situation significantly by doing a little refresher on house training, treating them like they are a puppy all over again and re-training them where to go. In other cases, if they are using the same spot to relieve themselves over and over you can at least contain the mess by placing absorbent pads in the areas he is urinating.
"Incontinence" medically refers to a pet leaking urine without being aware - it usually happens when they are sleeping or otherwise very relaxed. If you haven't witness which one is happening, it could be either. True incontinence can be caused by urinary tract infections, diabetes, kidney disease, and bladder or urethral stones, among other less common causes. Some of those problems can be easily managed and the situation improved significantly. Others are not so easily managed, and, knowing that they are present may help you make a difficult decision to let him go. The best way to differentiate between all these different causes is for the vet to test a urine sample (at minimum) and also some blood work. Those diagnostics can give you a vast amount of information on which to base your next decision.
In male dogs, true incontinence is actually quite uncommon, and I am doubtful that the PROIN would help. Most commonly, urinating in the house is either medical (like infection, stones, or "whole body" disease) or behavioral (like senility or loss of house training).
I sure hope this helps!