If you are all thumbs with a rasp, even one with a handle, or if even the finer side of the rasp is a little too much for what your horse needs, try using different grades of sandpaper. It can be a bit awkward, as the regular sandpaper holders are not the shape of a horse’s hoof, so you will probably have to cut a piece and do your best to wrap it around the hoof. Just the same, I have found during this last trimming round that doing a little sanding when there is the tiniest bit of roughness has helped Miles feet to stay beautiful.
An alternative to sandpaper, though not quite as specific to a particular part of the hoof, is riding your horse in an outdoor arena with a sand footing. This accomplishes much of the same thing and is good overall for the horse and its hooves.
Hooves R Us 