My daughter's cat urinated on an expensive marble fireplace slab. She poured hydrogen peroxide on the areas involved, left the liquid until it soaked in to dissolve the urine stains.
You need to be very careful when using peroxide - it is a bleach & will take color out of fabric, carpet etc. I've tried soooo many products, with no joy at all. The stain & smell comes back. The only think I've found to work is a recipe I got where I mix up a recipe myself when I need it. I found it at www.caturineoff.com - it's brilliant.