Truthfully, the only thing I've seen to truly make yourself invincible in D&D means either Pun-Pun or simply not existing in the first place.
Agreed, or a Water Elemental Dry Lich
Say what now?
Completely undetectable because what is dry water? Nothing
i believe that would be a can of dehydrated water, as per space quest 1....
But what if it's dry, as in martini? Wouldn't that just make it a Liquor Elemental Lich?
which promptly brings us to a portable hole full of beer
and a drunken master liquor elemental dry lich, on the rocks, of course.