Scratching furniture has two reasons, one is, as already described - to keep the claws in good nick. The 2nd is as a form of scent marking behaviour. Cats have scent glands between their paw pads & scent is deposited during scratching sessions. The most common places for this type of scenting behaviour, are near doorways & main walkways (in the house) to leave a message about ownership to other cats. If simply making it unpleasant to do that behaviour in that place & providing a suitable substitute does not work, then there is another option. You can change the type of marking behaviour using pheramones. They are available in a pump spray from your vet & have full instructions. (Not the diffuser) You are using facial pheramones to replace the ones that are left by the feet & incidentally this also works on those left by urination. These facial pheramones are usually deposited by your cat rubbing their head on you, doorways & other objects. The spray does not smell much to us & is mostly safe on furnishings. However certain places in every house are always going to be vulnerable & covering them up with something designed to be scratched on or that can be easily & cheaply replaced can be a sanity saver! Best of luck.