This is just a idea that really works for my cats. My husband bought a new cloth computer chair...and of course all 5 of my cats were all over it at once.
I wrapped bubble- wrap packing material around the back of the chair and continued it all the way around (front and back), because as mentioned before, tape doesnt stick well to cloth. Each one of my cats tried scratching on the bubble-wrap and immediately disapproved of it and the popping noise it made and now they completely avoid that chair!
It might look a little funny, but you get used to it in no time! And after awhile the bubble-wrap can be taken off and the cats will remember they didnt like it. If they continue after the wrap is taken off, put it back on for awhile longer.
It's safe, easy, and painless!