Kapus, method to turn the shield off depends on how it is actually spawned to the game world. If you took Leaf Shield as example, just give an inventory item to the player when the shield is activating. An item whitch does nothing and players are unaware of it. When you fire, check for that item and go in a state when you disable shield and take the said item. Look closely through Leaf Shield coding if you do not really understand what I am talking about.