breastwork vs picket fence

breastwork

noun
  • A parapet. 

  • A fortification consisting of a breast-high bulwark; a parapet. 

  • Breast augmentation. 

  • A railing on the quarter-deck and forecastle. 

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