foolproof vs unreliable

foolproof

verb

  • To render foolproof. 

adj

  • Certain to succeed in all eventualities, or claimed to be so; infallible. 

  • Protected against, or designed to be proof against, misuse or error. 

unreliable

adj

  • Not reliable. 

How often have the words foolproof and unreliable occurred in a corpus of books? (source: Google Ngram Viewer )