bombproof vs foxhole

bombproof

noun
  • An air-raid shelter, a structure designed to give protection against air raids and bombs. 

adj
  • Sufficiently strong to resist the effects of a blast from a bomb. 

verb
  • To make resistant to bomb blasts. 

foxhole

noun
  • A small pit dug into the ground as a shelter for protection against enemy fire. 

  • The burrow in the ground where a fox lives. 

verb
  • To dig a military foxhole into, or convert into a foxhole by digging. 

  • To drive into a military foxhole. 

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