Pass rope around the post/rail; cross free end under the standing part (portion of rope connected to the horse's halter). 2. Form a loop, going over and then behind the standing rope. 3. Make a second loop in free end, keeping it near first loop, and pass it over standing rope & through first loop. 4. Set or snug the knot by pulling on both standing rope & second loop. To untie, simply pull on the tail end of the rope.