Certain to succeed (8)
'certain to succeed' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sure-fire that I've seen before include "Certain of success" , "Dead cert" , "Infallible" , "Certain to succeed - a positive conflagration?" .)
(Other definitions for foolproof that I've seen before include "Not liable to failure" , "Not admitting failure" , "Certain" , "sure to work" , "Can't be misinterpreted, even by simpleton" .)
'certain to succeed' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for surefire that I've seen before include "Always effective" , "certain to succeed" .)