Wiktionary
sure-fire
a. certain to work alt. certain to work
WordNet
sure-fire
adj. certain to be successful; "a sure-fire way to get rich"
Usage examples of "sure-fire".
A sure-fire page one barn burner that implicated the KGB in the murders of Communist ultranationalist Yegor Kolokoltsev and his henchmen!
It wasn't a computer, but it was still a sure-fire sign of superiority in the middle of a refugee camp.