Moving a castle that has taken root is more difficult than breaking a mountain.
[CONT]: Sentinel (You may only have up to four cards with "[CONT]:Sentinel" in a deck)
[AUTO]: [Choose a card from your hand, and discard it] When this unit is placed on (GC), you may pay the cost. If you do, choose one of your units that is being attacked, and that unit cannot be hit until end of that battle.