Although you would normally use a deodorizing dog urine spray bought from a pet store to clean up urine stains, a stronger mixture of ammonia and talc chalk is more recommended for limestone rock flooring - especially as sedimentary rock like limestone has a tendency to absorb excess fluid. With this in mind, you need to mix together your ammonia and talc chalk in a hard-wearing plastic bowl until it reaches a gloopy paste consistency. If you think the mixture is too thick, add more ammonia. Likewise, if it appears too thin, add a touch more talc chalk.
Before you apply the poultice mixture to the urine stain, dampen a clean cloth with cold water and dab at the area you're working on gingerly. Don't make the mistake of rubbing fiercely - this will only cause the stain to spread and worsen further. Once the area is nicely dampened, use a spatula to spread the poultice mix onto it. Avoid applying it too thickly - a thin layer that you can't see through is satisfactory.
Once the poultice has been applied, cover the area clearly with a plastic wrapper, taping it down at the edges. Leave to set for 24 hours before removing the plastic wrapping and scraping off the hardened poultice. Use cold water and a fresh clean cloth to wipe the area once again and remove any residue. You should now find that the urine stain has been completely removed and the odor has disappeared.