Alcohol based perfumes - spray them with it.
It's illegal for anyone to own more than 2 cats in a residential area.
Aspro kills cats.
Crossbows arent accurate, so that would be illegal and inhumane. I catch anyone doing that to a cat and I'll do it to them.
You want to keep cats away ? Hide a few car speakers in the darket places of your garden. Hook them up to a stereo. Get a recording of a dog barking. See cat, play sound track.
Cats will only mark where there is a cat like smell already. Use the cat sprays that mask odors, never have the problem again. If cats cant tell the difference between your foot odour and cats piss, then i'd suggest your feet have a problem.