I had a problem with the cat jumping up on the window sills of our new house, marking the walls and leaving scratches in the paintwork. Short of murdering her, I pondered other alternatives. My first idea was to place a dozen set mouse traps along a sill until one morning lying in bed in that zone where solutions pop into your head. I came up with this great idea. I have cut lengths of plastic conduit (plastic down pipe would also do the trick) the width of the window. The cat jumped up on one of them causing the pipe to fall and giving her a fright at the same time. She hasn’t attempted to jump up since.