We stripped out all the carpet and pad, and the unit still wreaked of cat urine.  

Purchase price: $212,000 Cash invested: $46,000 Sale price: $325,000 Found a great 2013 SFR in an A class suburb that was mostly interior cosmetic.....IE smelled like cat urine or smells like money!!

I just put one property on escrow which was also in a very bad shape - strong smell with cat urine and I had to replace all drywall and existing flooring.As I am waiting for my escrow to be closed, this came into my attention.

He would email me these huge rambling messages at 3am (4 Loki fueled I'm sure) about how I deceived him about no previous pets in the unit because he could smell the urine.

After moving in they began to complain of a cat urine smell (which does not exist) and demanding that I replace the carpeting.  

Hire someone professionally locally to work for you and oversee manage the project (a construction manager).Some examples I can provide having worked in the construction industry is - soda bottles filled with urine in the walls, food thrown in the walls, throwing coffee down duct risers, sheetrocked over outlets providing fire hazard...

The urine will soak into the padding.

I am working on a home that has a horrible pet urine smell.

And in my experience with tenants , horse urine is worse than cat urine

In between my agent and I would walk houses where human feces was smeared all over walls, flea infestations were so bad you had to spray yourself down in the front yard when you came out, and rugs with years of dog and cat urine baked into it.