I have two house cats (rescue cats) (they NEVER go outdoors). They are not the best of friends. I also have four litter boxes which are cleaned at least 8 times a day. Still, these two cats don't always use the easily accessible litter boxes and will pee on my wood floors. I immediately clean up any urine and finish it off with a mixture of water and vinegar - then let it dry before the cats are allowed in that area. Sometimes the cats will pee in the same spots, sometimes they pick new spots. What can I do to deter this behavior? Thank you.