All rope knots, no matter how expertly tied, eventually fail. A solution is the addition of a double constrictor knot. The knot, which is tied with p-cord or string, binds objects together and can concentrate pressure over a relatively small area. For instance: Lash the tag end of an anchor knot to the main line for extra strength after repeated dunking. Finish the end of a rope to prevent fraying. Cinch a gear bag by tying the mouth closed. Here's how.