The password was given to me by a man who died in the dungeons of Arrakeen. You see, that is where I got this ring in the shape of a tortoise. It was in the suk outside the city where I was hidden by the rebels. The password? Oh, that has been changed many times since then. It was "Persistence." And the countersign was "Tortoise." It got me out of there alive. That's why I bought this ring: a reminder.
Attributed to: Tagir Mohandis
From Chapter 31 of Children of Dune by Herbert, Frank