This is more related to gardens, but I think is could be very helpful for people trying to keep cats away from specific areas of one's yard.
I've found cat dung in my front yard flower bed and other areas of the yard. Looking around the web, I found that many people say that cats don't like citrus. Using lemon or orange oils or peels, they are to be scattered in the areas that you don't want the cats to be. If it rains, it can be washed away, so reapply if it does rain. Supposedly after some time, this will deter the cats, and they'll stay away, even without the citrus.
If anyone has tried this, I'd love to read about your results.
I just sliced several lemons in half and scattered them in the flower bed and the bad corner of the yard. We'll see how it goes.