Performing the technique
In order to perform Gale Guarding, the opponent must be knocked off the stage. While they are recovering, the player must run, short hop or full jump off the stage, and then throw the Gale Boomerang directly at the ledge in a straight line. If done correctly, the boomerang will bounce off the stage, fly directly through Link, and pull the opponent away from the stage. This technique is best used against opponents with poor recovery.
A demonstration of Gale Guarding can be found here.
A glitch may occur while Gale Guarding in which the Gale Boomerang flies through the ledge and continues to fly through the stage, immediately entering its second phase. The boomerang will not return to Link, and instead will continue to fly on its path until it disappears. However, the boomerang will always be reusable even if this does occur, and it will only act as if Link had normally missed the boomerang on its return trip.