Marilyn said::
I've tried spraying water on them, but as soon as I pick the hose up and turn the water on, they dart away before I can spray them with the jet spray. 
Sounds as if it's working then!
I do understand that cats can be a problem, mine made firends with one of my neighbours cats, and would be in and out of her house all day as we had the same type of magnetic cat flaps, as soon as I knew it was a problem I took our flapout and replaced it with a microchip one, that way I could take the magnet off his colar and he couldn't get ino their house and no other cats could come into ours. And I told her that our cat is scared stiff of rustling plastic bags and tin foil. Russtling that sends him straight home! Might be worth putting some tin foil/plastic bag flags in your garden to see if that works?
