Here and there you'll see an immovable 'stationary shield', which behaves pretty much like a Jackal's shield. It deflects small-arms fire but will get wiped out by a plasma ball, or by an explosion. You're unlikely to use these much, but occasionally you can exploit the fact that enemies can't see through it. Crouch down behind the shield and you'll be able to watch the enemy through the shield, yet they don't see you. Could be handy for launching a surprise attack!