This question came from the Garage Journal today and unfortunately we have personal hands on experience with it. What is the best way of dealing with a concrete slab that has been used as an animal toilet?
First and foremost clean the concrete as best as possible and make sure you neutralize any bacteria, germs, etc. Unfortunately that did not help with the odor. In our particular case some tenants had just let their animals go wherever they wanted.
A painter told us to use Kilz Brand primer and it worked very very well!