We've tried the sprays. None of them worked. What does work is double sided tape. PetSmart sells special double sided tape that is designed to stick to furniture without damaging it. We use it on one particular chair that one of our cats like to scratch. The cats don't like the feel of their paws sticking to it. Eventually the realize that isn't a good spot to scratch and they stop. This won't stop them from scratching things...just that one sticky thing.

I agree that a good cat tree and scratching posts are essential in any cat home. But sometimes the cat doesn't care if he's scratching a post or a chair or a speaker...it all feels good.