mindful vs on one's guard

mindful

noun
  • As much as can be held in one's mind at a time. 

adj
  • Being aware (of something); attentive, heedful. 

on one's guard

prep
  • In a watchful state; alert; vigilant. 

How often have the words mindful and on one's guard occurred in a corpus of books? (source: Google Ngram Viewer )