It only tends to be the dominant cat in the area that leaves their poo around, the other more submissive cats will bury their poo. I tend not to get cats pooping in my garden, despite having a dog (that would dearly love to eat next-door-but-one's cat). The damn cat will saunter through the garden and shoot to the end when the dog comes out, and sit the other side of the fence laughing at the dog. Or it did until it found out the pole my brush is on is telescopic! One prod and now all I need to do is appear at the bottom of the garden and the cat is off.
If you can catch the cat in the act, squirting it with very cheap beer works a treat (and I mean the really cheap stuff I buy to make beer batter with), as cats hate being wet and sticky, and they get a bit drunk when they clean themselves, unlike humans cats don't like getting sozzled, and will tend to avoid the area in future. Silent roar didn't work for me (although when my Husband accidentally reversed over a cat that had been sleeping on top of a wheel, cats avoided the area for ages). Some interesting ideas though.