This is a common question, one tactic that a neighbour of mine swears by is to use a citrus smelling cleaner on furniture. Citrus is a smell that cats are well known to dislike, so my neighbour has a piece of furniture in the conservatory which is old and left untouched and the furniture which they want to kept scratch free smells like citrus.
The cat goes for the furniture that doesn't smell like citrus.
