Posted: 22/10/2013 at 13:31
I really can't see the harm in cats sunbathing on you shed roof. If you don't want them sharpening their claws on it, give them an old door mat or a piece of wood. You could also get a second sonar and place it as you need.
The only foolproof cat scarers are
a) a dog but that won't protect your shed roof
b) a water scarecrow which sprays them when they pass a sensor. Works on foxes and herons too. Google the name for info.
You can also spray them with a water gun but you have to be there all day every day.......