keep guard vs patrol

keep guard

patrol

verb
  • To go the rounds of, as a sentry, guard, or policeman 

  • To go the rounds along a chain of sentinels; to traverse a police district or beat. 

noun
  • A movement, by a small body of troops beyond the line of outposts, to explore the country and gain intelligence of the enemy's whereabouts. 

  • Any perambulation of a particular line or district to guard it; also, the people thus guarding. 

  • A unit of a troop, usually defined by certain ranks or age groups within the troop, and ideally comprised of six to eight members. 

  • The largest division of officers within a police department or sheriff's office, whose assignment is to patrol and respond to calls for service. 

  • A going of the rounds along the chain of sentinels and between the posts, by a guard, usually consisting of three or four men, to insure greater security from attacks on the outposts. 

  • The guards who go the rounds for observation; a detachment whose duty it is to patrol. 

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