belt and braces

/B EH1 L T AH0 N D B R EY0 S AH0 Z/
noun
  1. 1

    Redundancy affording mutual backup in the event of one system failing.

    โ€œHe believes in belt and braces, booking flights from two different airports on different airlines for important trips.โ€

Source: https://en.wiktionary.org/wiki/belt%20and%20braces