foolproof
adjective
[ ˈfuːlpruːf ]
• incapable of going wrong or being misused.
• "a foolproof security system"
Similar:
infallible,
never failing,
unfailing,
unerring,
dependable,
reliable,
trustworthy,
certain,
sure,
guaranteed,
safe,
sound,
effective,
efficacious,
tried and tested,
watertight,
airtight,
flawless,
perfect,
sure-fire,
