Incapable of failing (9)
I believe the answer is:
foolproof
(Other definitions for foolproof that I've seen before include "Infallible" , "incapable of going wrong" , "Not admitting failure" , "Certain" , "Completely safe" .)
I believe the answer is:
foolproof
(Other definitions for foolproof that I've seen before include "Infallible" , "incapable of going wrong" , "Not admitting failure" , "Certain" , "Completely safe" .)