Security Blockade is a uncommon Enchantment — Aura card from Return to Ravnica (RTR), collector number 20. Current market price: $0.07 (foil $0.40), TCGplayer market prices via Scryfall.
Enchant land When this Aura enters, create a 2/2 white Knight creature token with vigilance. Enchanted land has "{T}: Prevent the next 1 damage that would be dealt to you this turn."