keep a tight rein on someone/something
keep a tight rein on someone/somethingor
keep someone/something on a tight rein
COMMON If you keep a tight rein on someone or something or keep them on a tight rein, you control them firmly and carefully. Note: The reference in these expressions is to a rider using the reins to control a horse. It is said that he kept a very tight rein on his daughters, and that he was a very strict father. The recession has forced people to keep a very tight rein on their finances when on holiday. Her parents had kept her on a tight rein.