Hey Susan, I'm sorry to hear about your cat's diagnosis. I have a 16 year old boy living with kidney disease (diagnosed 3 years ago) and it is manageable, but also sad to watch my once lively boy turn into a geriatric old man. Our boy used to be an outdoor cat, too, but now doesn't really have the energy to go wandering.

That said, your boy might be different. What I'm getting at is, do whatever you need to do that gives you peace of mind. A microchip isn't a GPS chip, though, so it would only be helpful if someone found him and returned him to a vet clinic. https://www.catster.com/lifestyle/cat-tracking-chips/ for more information.

You could get a GPS tracker on a collar, we have a few here: https://www.catster.com/lifestyle/cat-tracking-chips/

Or you could try to convert him to an indoor cat. Just keep caring for him the way you do and hopefully you don't have to worry about him wandering away, and hopefully you have many years left with him, just managing the kidney disease. <3