Ive found a few things get rid of the little bastards.

Lion shit! (no joke) get yourself round the local zoo and get some, you will never see a cat again.

Lemon essance, spray this where you dont want the cats, they hate it.

or the super soaker max infusion helix Blaster V, cats hate water, and this fires 2 jets in a spinning motion, its fantastic, the kids patrol the garden with it keeping the cats out.