Why not give engineers hand shields with the same limitations as a stalker cloack? On the activation key of the ability, the engineer raised his shield, losing the ability to shoot, but completely protecting himself in front, except for his legs. And in the unraised state, the shield would protect the left flank. Shield models can be similar to mana turret shields.
not really something I think the engineer would traditionally use. I would suggest more automated sytems or turret types like placable flak turrets or, if you need defensive options, a shield wall that has a firing port in it. Engineers arent really meant to be frontline fighters, so it doesnt make sense to me to give them a MAX esque riot shield.
