waterproof

1. (figurative) Incapable of failing; unassailable.Examples: "The only waterproof plan and the one increasingly adopted by leading trades is the consolidation of the interests of all parties in a scheme of amalgamation."; "Especially within an international framework, guarding this process is of the utmost importance. The eyes of the world are focussed on the action at hand and demand a waterproof plan and execution."; "Unless you have a 100 percent waterproof plan to defraud insurance companies, I would suggest you don't do it."figuratively