Horrendous cat pee problem

[Janett Fisher]

I rented my house to a retired military vet, who claimed he knew what clean meant. When I got the keys to the house back, I had to enter with vesperator masks, as the smell was so bad. The entire house was covered in urine. I tore all of the flooring out, including tile in the kitchen and hardwood stairs. I washed the walls with a urine gone solution and vinegar. I then used Kilz everywhere. In the basement I used my nose and sniffed along the wall - marked several areas and removed the drywall in those sections. All baseboards were removed too. I run an ozone machine every time I am there.

I thought I got it, painted the walls, installed new floor and baseboards. And now the AC failed and the smell is back - only in the basement though. There are pockets of pee smell and overall the area just smells, and not pleasant. 

I don’t know what else to do. I wanted to rent it again, but I may need to sell. However, I won’t be able to with that smell either. I am about 20k deep in the renos. I can’t really afford to rip everything back out. Any suggestions?