Some people on this thread need to calm down . . . What the?
I've used this motion-activated sprinkler against marauding dogs, it works well.
Amazon.com : Contech CRO101 Scarecrow Motion Activated Sprinkler : Lawn And Garden Sprinklers : Patio, Lawn & Garden
Couple of times should do the trick.
And, YES, a cat can fall right through a canvas top, if it's brittle and old. Happened to hubby's 911 . . .