Source : WordNet®

bulletproof
     adj 1: without flaws or loopholes; "an ironclad contract"; "a
            watertight alibi"; "a bulletproof argument" [syn: {ironclad},
             {unassailable}, {unshakable}, {watertight}]
     2: not penetrable by bullets; "bulletproof glass"; "bulletproof
        vest"

Source : Free On-Line Dictionary of Computing

bulletproof
     
        Used of an algorithm or implementation considered extremely
        {robust}; lossage-resistant; capable of correctly recovering
        from any imaginable exception condition - a rare and valued
        quality.  Synonym {armor-plated}.
     
        [{Jargon File}]