Oh boy, I'm no help at all. My dogs have all but ruined my back yard grass, going back to before the bullies. It used to be nice, really it did. I've all but given up. What they ruin I just replace every few years with new sod. During puppy potty training we did take them to one side of the yard. Problem with that is that area will get ruined pretty dang fast. Now I have 4 and they poop and pee wherever their bodies take them. I really don't care where they go as long as it's on the grass.
I know there's stuff out there but I've never really looked at it before....just not worth my time. Unless you plan on keeping him on a leash all the time, I doubt he'll continue to go in the same spot, dogs like to mark and wander.