Recently I experienced a bit of a problem with one or two neighbourhood
cats which were engaged in a literal pissing match, partly involving my
back yard. A new, pure white cat had recently arrived, and was trying
to establish territory by scent marking; the residents were resisting by
Faced with a back yard reeking of cat pee, I at first tried scent
deterrents, making my back yard at first reek of Jeyes Fluid, then of
garlic essence. Neither worked for long, and nor did lemongrass oil, or
citrus oil (though the yard smelled quite nice). Then I tried putting
one of these devices out, a couple of feet away from where a cat jumping
down into the yard would land.
The yard is monitored by a CCTV camera, so I was able to see the
result. A couple of close encounters with a horrible hissing monster in
the dark was enough; the pissing match has been postponed indefinitely.
So, might I suggest deploying one of these things near where you'd
prefer the cat not to go? All it does is hisses loudly and unexpectedly
close to the cat, which is apparently a hell of a shock for a feline,
though it is otherwise harmless. They soon learn to avoid it, though,
and it is less intrusive than scent deterrents.
 Cats in my neighbourhood have a sadly limited lifespan, mostly due
to traffic. A pure white individual, even a widely ranging one, would
likely live longer due to being more visible to traffic.