A sanding sponge (AKA Sanding Block) is an easy to use, light weight and flexible sponge that comes in varying degrees of abrasiveness. Just like sandpaper, you want to look for a medium to course grit for lightly sanding your horse's hooves. They are more flexible than rigid sanding blocks and can be rinsed and reused when you are finished. You can find them at almost any hardware store.