Ride Herd On Meaning

(transitive, idiomatic, US) To supervise a group of people, such as workers, and/or their actions, i.e. their work.

Example:   But Rabbit feels as though he owns it all, showing up at the showroom day after day, riding herd on the paperwork and the payroll [...]. - Rabbit Is Rich by John Updike
  As the new editor, his job is to ride herd on the staff and check on the tone of the articles.