For long downhill slogs, like Whitney, I sometimes do a double over my instep if my feet are slipping forward. Whether my foot slips on any given day depends upon lots of factors. It isn't always necessary, so I don't adjust them until after I've got down a mile or so.
Sometimes I double over the laces at the instep. This has the benefit of "locking in" the heel, and it also means the last 2 or 3 laces can be a bit looser, providing better circulation.
