To keep a tight rein on somebody/something
Definition 1 of 1
Pro Tip 1/3Figurative Sense
This phrase is used figuratively and implies control without physical means, like using real reins. 
The CEO keeps a tight rein on the company’s finances to ensure stability.
Pro Tip 2/3Metaphoric Origin
Originates from horse riding where reins are used for control; thus suggesting hands-on management or supervision. 
The director keeps a tight rein on the movie production to maintain his vision.
Pro Tip 3/3Strict Supervision
Emphasizes strict supervision or limitations placed on behavior, often to maintain order or discipline. 
Teachers must keep a tight rein on students during field trips.