Fortitude

The boomerang clause changes the entire math of the protective Aura. Most Auras of the era were a tempo gamble: you committed a card to a body, and the standard answer (kill the host) buried both in the graveyard for a clean two-for-one. This one refuses that exchange. When it dies with its creature, it bounces back to your hand, so the only thing your opponent ever achieves by killing the enchanted body is forcing you to spend again and reattach to the next target in line. The protection itself is cheap, drawing on a Forest per activation, and the recursion makes it a reusable insurance policy rather than a one-time investment: green rarely had access to persistent attrition tools this early, when its defensive game leaned on raw toughness instead of answers that stick around. The land cost is the counterweight that stops the regeneration from being free. Every shield drains a Forest off your board, so a creature that walks through repeated sweeps is also one you are paying for in mana development. The sacrifice and the return clause pull from opposite ends of the same idea, one ensuring the protection can never be stranded on a corpse, the other ensuring it never comes without a price. It looks like humble combat insurance, but an Aura that cannot be neutralized by killing its host is a sharper solution to card disadvantage than the rate lets on.