Lori I'm sorry you are going through this again. I know when we had that issue a few months ago I thought I was going to lose my mind!! I wish I had some great advice to offer but I don't.
Ours were doing it in the fall when we had the windows open. The ferals that I feed were spraying and marking their territory outside and mine felt the need to mark theirs inside. Mine finally stopped after we closed the house up. I'm not looking forward to Spring!!