Rule #3: Don’t drop the rope.
This rule is by the far the simplest conceptually--just don’t drop the rope. However, this may be cumbersome in practice, especially when changing over the anchor on a single pitch climb as you thread the rope for rappel. A recent incident at Yellow Bluff, Alabama, where a climber dropped the rope and found himself stranded at the anchors, sheds light on just how easy it can be to make this mistake.
Many climbers tie the rope off to their harness in some way before untying their figure-8 knot to thread the rope for rappel, often tying 2 or 3 knots in the process of changing over the anchor. I recommend the same approach whether you are rappelling or lowering off. The following steps minimizes the amount of tying and untying that goes on:
1) Starting at your figure-8 tie-in knot, pass a bight of rope through the rappel rings.
2) Tie a figure-8 on a bight with this bight of rope on the side of the rings opposite from your tie-in knot.
3) If you will be lowering, clip this new figure-8 on a bight to your belay loop, untie from your tie-in knot, and lower off. If you will be rappelling, untie from your tie-in knot and lower the figure-8 on a bight to the ground. If you have been following my recommendations from rule #1 (always know where to locate both ends of the rope), then at this point you will have a stopper knot in each of your rappel strands and you will have avoided any chance of dropping the rope.
Another place where you might find yourself without a rope is on a traversing multipitch rappel, particularly if you and your partner arrive at the anchor and let go of the ropes, watching helplessly as they swing away from you to a point under the plumb line of the anchor above. This can be mitigated by keeping a firm grasp on the ropes (the prussic hitch you used to back up your rappel is useful for this--you did use a prussic, didn’t you?) until you’re ready to thread them. You can even save yourself a step by beginning to thread the rope while your partner is rappelling.
You may also find yourself in a similarly unpleasant situation on a multipitch rappel under very windy conditions where the rope ends may whip around violently and get stuck on a rock feature some place far away and likely inaccessible. In the case of severe wind, the safest course of action is to stack each rope end into a sling hanging off either side of your harness (known as “saddlebags”) so the rope can feed out as you rappel without whipping around in the wind. Of course, if you’re following rule #1 (know where to locate your rope ends), then you’ll have already accounted for this since you don’t want your rope ends stuck around a corner somewhere.