I like the idea of a 2h move that when it depletes shield up defense bar, it also does HP damage to the shield item itself. So the shield user can only block this ability so much before shield his shield is destroyed and then he cannot use shield up. (this follows up my other thread where shields have armour that only effects arrows dmg)
Down side is people carrying an inventory full of shields, BUT I think equipping shields mid fight might need to be disabled currently anyway as its pretty OP if say my archer had a macro to switch bow to shield when being attacked.