balustrade vs picket fence

balustrade

noun
  • A row of balusters topped by a rail, serving as an open parapet, as along the edge of a balcony, terrace, bridge, staircase, or the eaves of a building. 

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