we done this with carpet grippers neighbours complained, but spoke to someone from the rspca said its perfectly leagal as long as you have a warning up, its not for the cats the warning but potential burgulars they said as they can sue you without a warning sign. But intentially was to keep cats out! But took them down to keep one of the neighbours who at the time had recently moved in and they complain about everything there pretty nosey neighbours they even complained once our petals from rose bush fell into there gardren, and they said hope we are not begin petty! Me mum put them straight lol