Decending Johannesburg, I finished one rappel where it really looked like it was pretty certain that the rope would cause rockfall when we pulled it. Ordinarily, I'd clip into the next rap anchor while waiting for partners to descend. I didn't like the location at all, so I walked right on a ledge and built a temporary anchor under the lee off a projecting rock. We all clipped to that. When we pulled the rope, a positive rain of rocks scoured the rap station to my left. I guess I made a good call in that one.