When you cast this spell, choose an object within close range that has combined hardness and hit points no greater than twice your caster level. Until that object is destroyed, you lose line of sight to it, you lose line of effect to it, or you come within 10' of it, you are invulnerable. While invulnerable, attacks cannot hit you, you always succeed on saving throws, and you cannot take damage. A Spellcraft check to identify this spell also identifies which object is sustaining it.