We have a senile 17 year old female and a 2 year old male. One of them (I suspect the poor female) is occasionally peeing in one spot. No big deal but it has run into the heat ducts and it is impossible to clean and remove the smell. Is it true that if one cat pees in a spot, the other will follow suit based on the smell? I try to watch them closely when I'm at home but can't be sure who is actually doing it. I will have to have the ductwork cleaned and possibly replaced in that spot and in the meantime don't let anyone in the house. Should I wait until the female goes to kitty heaven before having the work done or before? My husband and I are at our wit's end!!