I should have suggested this a long time ago, but wouldn't it be amusing that if a creature with 1 | X (X = any HP, unimportant) attacks this shield that they're automatically rewound back into the deck (think of a creature running away back to the owner)? It'd prevent deck-out on their part, but it would also nerf this card into oblivion if you managed to nullify a creature to 0, only for it to be sent back into the enemy's hand to be reused again the next turn...