padlock vs tie down

padlock

verb
  • To lock using a padlock. 

noun
  • A detachable lock that can be used to secure something by means of a sliding or hinged shackle 

tie down

verb
  • to secure as if with a rope or hook. 

  • to constrain, or to confine within set limits. 

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