Machina Defense Perimeter

While you control a Level 7 or higher Machine monster, your opponent's monsters cannot target Level 6 or lower Machine monsters you control for attacks, also your opponent cannot target them with card effects. If a face-up Machine monster(s) you control is destroyed by battle or card effect: You can target 1 Machine monster in your GY; add it to your hand. You can only use this effect of "Machina Defense Perimeter" once per turn.