Triamid Fortress

All Rock-Type monsters on the field gain 500 DEF. "Triamid" monsters on the field cannot be destroyed by card effects. If this face-up card in the Field Zone is sent to the Graveyard: You can target 1 "Triamid" monster in your Graveyard; add it to your hand. You can only use this effect of "Triamid Fortress" once per turn.