Human barricades.
WAIT, let me propose the idea before you redicule it.
Basically, its a concrete/steel wall about the size of a barricade, but with 450hp. It will be a structure which you can only build one of (Defend that critical armoury/medi during SD from snipers) but can be rebuilt three times. It CANNOT be repaired (this could lead to more tense games where you are relying on 'that' bloody wall to please PLEASE hold so you can buy your luci and bugger off).
It would basically be a large shiny grey rectangle wityh 'steely' textures.
What do you think ? Or perhaps it could only be built during SD ?