fencepost vs picket fence

fencepost

noun
  • A post which helps hold up a fence. 

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 fencepost and picket fence occurred in a corpus of books? (source: Google Ngram Viewer )