Castable Spell that Gives Invulnerability but NOT Spell Immunity?

I know there is a neutral invulnerability spell that passively makes you always invulnerable.. but i need something that can be turned on and off and use mana possibly and show a spell graphic.. something that can either be activated or cast on another person.
Any such thing?

if you want invulnerability as doesnt-get-hurt-from-physical-damage then you can just take any armor++ target spell (unholy frenzy, inner fire, etc) and set its bonus to 999999999999.

Would Manashield work?
Or you could use Berzerk with modified 'Damage Taken' field.
Manashield and Berzerk have both the problem that the caster could still be attacked though it wouldn't take damage.

You could give Ethereal Form and/or Banish a try.
Those would offer both functionalities (active/targettable) but might have some side effects due to the ethereal classification.

If all that won't help you could trigger it.
Set unit classification to something that can't be attacked by regular attacks.
Add 100% evasion, spiked carapace, etc to the target unit.