There is a strong smell and feces on the floor during my quarterly maintenance checks, which likely means urine as well. 

I took a black light and saw a lot of urine and I can see a lot droppings.

First learn to deal with the pet urine:http://www.biggerpockets.com/forums/67/topics/48302-dealing-with-pet-urine-in-plywood-subfloorOnly an investor would be likely to buy such a house.

They believe the hurtle is SO BIG that becoming "rich" or "financially independent" is not within their realm.

There's old cat feces everywhere, noticeable urine stains, scratched up walls, black mold on the walls, rotten window sills, doors made out of wood and chicken wire that apparently were built to block off hallways, a tree partially through the roof in the living room, holes in the walls in some places, refrigerators that are beyond disgusting and vanities that are barely standing among other issues.The place has a lot of potential I think once it's cleaned up but I've never tackled this kind of situation before.

Urine?

Will allow de-clawed, spayed/neutered, FEMALE indoor cats (males tend to spray urine all over the house) and dogs on a case by case basis.

I am rehabbing a house with pet urine stains throughout the upstairs subfloor.

The best thing is to remove urine soaked wood. 

Do you research.My recent installation was in a home that had animal urine soaked carpet and minor urine soaked subfloor.