If it is particle board I would replace it.Here is a technique for getting rid of the oder for good,Remove carpeting, padding and other flooring around the areas you suspect urine has leaked into the subfloor.Apply an enzymatic pet cleaner (like Nature's Miracle) to the soiled areas and allow them to dry thoroughly for 24 to 48 hours.

You can let them know your pet peeves upfront and that may turn some away. 

Do you allow pets in your vacation rentals?  

In this post https://www.biggerpockets.com/forums/52/topics/384924-should-i-accept-tenant-with-1-cat-if-we-advertise-no-pets?

Do the tenants have pets, pay pet fees, no restricted breeds with your insurance company?

Are you allowing pets?

You CAN go by highest income, longest time on the job, pets or no pets and be within the law.

I screen tenants myself, so I can meet them and their pet. 

There are pet stains throughout the carpet and I don't know how to figure if the carpet is salvageable.

:D nice pet on the back, keep going.