Buy some Urine-B-Gone at Wal-Mart or the pet store. They sometimes package it with a small battery-powered black-light that will help you find the places Rover did his business.
If there are cracks in the tile you will need to replace them. If the grout is missing in places you are going to need to redo the grout and seal it again.
If there are cracks in the tile you will need to replace them. If the grout is missing in places you are going to need to redo the grout and seal it again.