Kingtree Cat Corner Scratcher Self Groomer with Catnip, 2 Pack Softer Cat Face Scratchers Wall Corner Grooming Massage Combs for Long & Short Fur Cats

These, or something similar, as noted by u/Helpful_Professor_33. Even four-legged cats love them, but they're great for tripods. As u/Helpful_Professor_33 notes, use Command strips to attach them. (I own my place, so I used screws, but Command strips work great if you're renting.)