covert baron vs sub rosa

covert baron

adj
  • Covert, under coverture; married. 

sub rosa

adj
  • Carried out secretly or confidentially. 

adv
  • In secret or covertly; privately, confidentially. 

noun
  • Covert surveillance video used to catch workers’ compensation applicants and show that they are in fact not injured. 

How often have the words covert baron and sub rosa occurred in a corpus of books? (source: Google Ngram Viewer )