Oh hold me back!! I am a cat lover and a cat owner but mine stay indoors. However,the rubbing the cat's nose in its mess doesn't do a thing! It's also pretty much too late to try and train kitty now. He's too old.
You might try laying down some tin foil in the area where kitty goes. This worked for my old gal who is now 16 and suddenly has taken to peeing in a large potted plant! Cats don't like the texture of tin foil. Another suggestion is to save your orange and grapefruit skins and put them in the corner where kitty pees. Cats hate the smell of citrus too. Might work. If kitty is old(10 years plus is considered a senior cat)it is most likely a problem with bladder incontinence as you mentioned. Just like us it happens to them too. A third suggestion is to man the area with a spray bottle in hand and when you catch kitty in there peeing, spray him/her.Cats hate the sound of a spray never mind the water.
Good luck..