slack off vs stand down

slack off

verb
  • To decrease in intensity; to ease off; to diminish; to die down. 

  • To be deliberately unproductive in one's work or study. 

stand down

verb
  • To wait; to stop pursuing, stop fighting, or relax from a heightened readiness posture. 

  • To withdraw or retire from a position or from a team. 

How often have the words slack off and stand down occurred in a corpus of books? (source: Google Ngram Viewer )