land mine vs strip mine

land mine

noun
  • A mine that is placed on land and designed to explode when stepped upon or touched. 

  • A piece of exercise device consisting of a pivoting tube attached to the ground to which a barbell can be fitted to lift it off the ground. 

  • A critical subject or situation with concealed or unpredictable implications. 

strip mine

noun
  • A mine where the material above the ore is removed (stripped) to expose it for removal and use. 

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