The most difficult substance to remove from wool rugs is cat urine, and this is due to simple biology.
Due to their desert origins, a cat’s urine is highly concentrated and contains very little water. If you own a wool rug that has had cat urine on it at some point, another cat may notice that the rug has been peed on before and will do it again. You can avoid permanent damage if the rug is professionally cleaned soon after the incident.