Wiktionary
triple check
n. An extra check or verification made a third time, usually with additional caution or attention. vb. To check again; to check with extra caution or attention; to verify or make sure.
Usage examples of "triple check".
Unless whoever's responsible for sending out the rescue crew is utterly barren of intelligence, they'll triple check everything before taking off.
It took some doing, asking for favors, fighting the urge to triple check every detail she'd already double checked.
We triple check that gear, Libby, because we know our lives depend on it.