below the belt vs over the fence

below the belt

prep
  • Of a punch, landing illegally, below the opponent's waist. 

  • Unfair; dirty; not according to the generally accepted rules. 

over the fence

prep
  • Entering, or having entered, the airfield in preparation for landing. 

  • Used other than figuratively or idiomatically: see over, fence. 

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