sheepdog vs usher

sheepdog

verb
  • To chaperon or shepherd. 

noun
  • A breed of dog, used for herding sheep. 

  • A breed of dog used for guarding sheep. 

  • A police officer. 

usher

verb
  • To accompany or escort (someone). 

  • To lead or guide somewhere. 

  • To precede; to act as a forerunner or herald. 

  • To guide people to their seats. 

noun
  • A male escort at a wedding. 

  • A doorkeeper in a courtroom. 

  • A person, in a church, cinema etc., who escorts people to their seats. 

How often have the words sheepdog and usher occurred in a corpus of books? (source: Google Ngram Viewer )