Nature's Miracle worked the best for me, too. At first I was not using enogh - it has to really soak down in the padding and I did not sop any up at first either as I wanted it to soak into the padding, baseboards and flooring - kept it wet for the first couple days and then dried it up and the odor was gone.

It can be really hard as you may not be getting all of the spots. Have you tried a black light? Just on regular one like popular in the 70's or there is one called a 'stinklight" but it costs more. If you put only this blacklight on at night - no other lights and literally crawl around the room with it - it will flouresce any areas with pee on them - even a spray or drops on the wall or floor board.

This is SOOO frustrating I know - went through it with my previous cats several years ago as we had a "geriatric ward" for awhile and they had problems with it to the end. Eventually - sorry to say - we did have to tear out sections of old carpet, padding and baseboards to get rid of the smell - then change furniture some so the bare areas were covered. We had to do it until the air smelled fresh. What we found was that it was mostly the WOOD that held the odor and what a relief to have it gone!!! So check baseboards, OK?? That might be your problem. And they are easy enough to replace if you have to