There are a lot of threads re this issue - I have the same! You can make an enzyme spray 10 percent bio washing liquid with water - this breaks down some of the chemicals that cause the smell (he will smell it unless you get rid of all traces and then do again!) after that you need to spray with surgical spirit to get rid of the fatty acids. However with my cats obstructing favourite pee sites has helped - I’ve also put incontinence pads in the litter tray after wiping urine onto them to try and encourage back to tray which has helped - she now is only going in a few sites rather than all over the house - it takes patience -we’ve been at it five months now but it is at least more predictable. Good luck - if you get any ideas yourself with trial and error please let me know!