The definite DO NOT's is to yell at the cat or spray them with a water gun. These actions just make the cat mad at you and the cat could scratch and dig more with a renewed vengeance. First, try placing a scratching pole in the problem area with catnip rubbed on the pole.
Another thought, fire-off one of those personal protection alarms when the cat does their nasty habit - hopefully, they will think scratching caused the noise. Last, call your vet about the pros and cons of declawing the front feet.