Invincible Marine on Outskirts

In Halo 2 on the level Outskirts, when you play with the difficulty level set on Legendary; there is a marine that can become invincible. This can only happen when you are driving through the tunnel on a Warthog and you have a marine on the rear gun. When you get to the area where the Covenant have positioned troops and ammo crates in the tunnel, see if you can get any enemy to shoot at him with Needlers. From then on, he cannot be killed.