Cats can be deterred by vinegar as they dont like the smell. I have read recently about using a watered down spray of vinegar and water to put off cats from going near areas. Cats dont like to be messy and there is usually a reason for behaviour like this. We had a problem with our cat recently where she suddenly started wetting indoors. We found that it was down to stress as she was being tormented by another cat outside and wouldnt go out. We gave her a litter tray and she happily uses that at night now.