Verbs

(v)bulletproofmake bulletproof“bulletproof the car”

Adjectives

(s)unassailable, unshakable, watertight, bulletproof, ironcladwithout flaws or loopholes“an ironclad contract”, “a watertight alibi”, “a bulletproof argument”
(s)bulletproofnot penetrable by bullets“bulletproof glass”, “bulletproof vest”