gatepost vs picket fence

gatepost

noun
  • a vertical post from which a gate is hung/attached. 

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