I've been having a problem lately with 1 or 2 specific male cats in the neighbourhood coming in to my house via my cat flap and scent marking/urinating on vertical surfaces to (I presume) mark 'their' territory.
My 3 cats seem to tolerate the main culprits, I wouldn't say they are "best friends" but they do hang out harmoiously out the back!
I don't want the scent marking to happen any more because the smell is really noticeable and disgusting. (the cats don't seem bothered or avoid those areas or anything, though).
Please can you give ideas of how I can stop these guys from doing this?
Edited to add: every couple of days I clean off any existing 'deposits' using disinfectant etc. I bought a UV light to show up where any specific 'deposits' are!
Edit 2: I'm particularly looking for ways that even if a 'stranger' does somehow get in the house.. how to get them to "not" scent mark, rather than how to stop them getting in, if possible, please.