bulletproof

a.
  1. Capable of resisting the force of a bullet; resistant to penetration by a bullet; armored; as, a bulletproof vest; a bulletproof window.
  2. designed so as to be resistant to abuse or misuse and incapable of malfunction under normal use; as, a bulletproof computer program.
  3. so well thought out as to be resistant to criticism or certain to succeed; as, a bulletproof plan.