Review on 🐾 CLAWGUARD Transparent Window Sill Protector - Ultimate Defense Against Dog and Cat Scratching, Chewing, Slobbering, and Clawing on Window Sills. Safeguard Paws and Maintain a Clean Home. (Clear 29.5 in. x 3.25 in.) by Trish Edens

They don't work well on old, deep windowsills. But the standard size of modern window sills fits better, but is not tight. The material, which is a mix of plastics, is as thick as plexiglass and fairly durable. It may scratch, but it won't break. The reason I pointed out it wouldn't fit snugly or on a deep windowsill is that if your pet/kid catches the edge they can snatch it right off the windowsill with little effort. It's held in place with the round M3 Dot. adhesive holder. I don't know if they will peel off the paint after prolonged exposure to the sun and then cooling, over and over again, but it's possible. All in all, it's not a terrible thing. But you may need to customize how it's placed, where it's placed, etc.