KEEP A TIGHT REIN ON SOMEONE OR SOMETHING

keep a tight rein on someone or something: translation

keep a tight rein onsomeone or something&keep a close rein onsomeone 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.