push back vs ward off

push back

verb
  • To postpone. 

  • To refute or argue against a position or an accusation; to express one's own view on a situation. 

  • To summarily expel asylum seekers, especially in violation of the principle of non-refoulement. 

  • Used other than figuratively or idiomatically: see push, back. 

ward off

verb
  • To avert or prevent. 

  • To parry, or turn aside. 

How often have the words push back and ward off occurred in a corpus of books? (source: Google Ngram Viewer )