1 general:: Phrase(s): keep a tight rein on someone or something [and] keep a close rein on someone or something Fig. to watch and control someone or something diligently. (Alludes to controlling a horse by a tight grip on the reins.) • The office manager kept a tight rein on the staff. • Mary keeps a close rein on her children.
McGrawhill's American Idioms And Phrasal Verbs