Equip the Stealth Gear and run through a guard. He will look in the direction you came from and say "Hmm. What was that?", with a question mark over his head. When he looks that way, get in front of him and take off the stealth gear. He will be alerted of your presence. When he has seen you, put the stealth gear back on right away, before he shoots. He will then be confused and start looking for you. You can do this as many times as needed. This also works with the search light area in the beginning of the game.