My cat is thoroughly put off scratching furniure by the application of a Bitter lemon product, but when I tried to keep him out of the Christmas tree with it, he was willing to stand in liquid puddles of it rather than desist from chewing on the shiny lights. (Thinks he's a dog: has chewed the wooden button decorations off my slippers, the metal handle of my capo has kitty teeth marks all over, chair rungs are a favourite, and he has almost chewed the leg off a small plastic dog I got him: nevertheless, the vet says his teeth are fine.)