Instant, 2W (3)
Common
Populate. Creatures you control are indestructible this turn. (To populate, put a token onto the battlefield that's a copy of a creature token you control. Damage and effects that say "destroy" don't destroy indestructible creatures.)
Illus. Mark Zug

10/1/2012: You can cast Rootborn Defenses even if you control no creature tokens.
10/1/2012: The creature token you put onto the battlefield as well as creatures that come under your control later in the turn will also be indestructible.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Extended (Type 1.X)
Legal in Standard (Type 2)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern