Holy cow: tank monks can be invincible for 1/5th of the time, using 1 skill. If the Beacon of Ytar passive is really back in as the unofficial notes for patch 14 indicate then that means almost a quarter of the time.
Tank builds for hardcore that use serenity, anyone?
Oh with Mantra of Healing shield being spammed too? Invulnerable monk? I think it can be done.