One of the last things you want when you water-ski is to watch your ski rope come untied from the boat that's pulling you. You need to secure your ski rope well, to prevent that possibility. A simple knot can grab the ski pole; for safety's sake you should also prevent the knot from coming undone.
Constrictor Knot, Two Half-Hitches
Make a constrictor by making two loops in the ski rope, about two feet from the end. Twist the top loop so it rests atop the bottom loop. Drop both loops over the ski pole and pull the rope's bitter end -- the one end of the rope -- to tighten the knot. To prevent the constrictor knot from capsizing, or coming undone, tie the bitter end to the ski rope with two half-hitches. To tie a ski rope to one of a boat's tow rings, tie the constrictor knot around the tow ring and use two half-hitches to secure the bitter end to the ski rope.