backstop vs picket fence

backstop

noun
  • A wall or fence behind home plate. 

  • A catcher; the position of catcher. 

  • The player who stands immediately behind the striking base. 

  • Something serving to bolster or support a cover story etc. 

  • A thing or a person put in the rear or in the back of something to reinforce, hold, support. 

  • A default arrangement that holds if all else fails. 

verb
  • To bolster, support. 

  • To serve as backstop for. 

picket fence

noun
  • A simple fence made from wooden pickets, connected by horizontal bars. 

  • A series of spaced perpendicular striations that occasionally occur in aurorae. 

How often have the words backstop and picket fence occurred in a corpus of books? (source: Google Ngram Viewer )