The staples are just there, not covered with anything, and I can't imagine how I could cover the staples with rope. (What would hold the upper layer of rope on? Wouldn't rings of rope sticking out from the pole encourage the type of hanging on the scratching post that could result in a nail getting stuck in the staple between layers of sisal and pulled out?) I made two scratching posts, and in the four years at my house and the four years at my mother's house, they haven't caused any problems. Mine has a very shaggy section from repeated use, but I've seen no injuries. I suspect it is just as easy for a cat to catch a claw in the sisal rope as on a small bar of metal (that is in a depression in the sisal, because we nailed them on but good). Actually, I strongly suspect it would be much easier for a cat to get a claw out of being caught under the staple than out of being caught in the sisal.
I have no memory of whether the sisal slipped out of our hands: it was too long ago. The wrapper wore gloves, and we occasionally stapled as we went. I suspect the sisal slipped out of hands, but I don't remember that specifically.