bullet-proof

 Capable of resisting the force of a bullet; resistant to penetration by a bullet; armored; as, a bulletproof vest; a bulletproof window.  [1913 Webster]

 designed so as to be resistant to abuse or misuse and incapable of malfunction under normal use; as, a bulletproof computer program.  [PJC]

 so well thought out as to be resistant to criticism or certain to succeed; as, a bulletproof plan.  [PJC]