keep watch on

keep (a) close watch on (someone or something)

To monitor someone or something closely. Keep a close watch on this pot so that the soup doesn't boil over.
See also: close, keep, on, watch

keep watch on someone or something

to monitor someone or something. Keep watch on the lady in the big coat. She may be a shoplifter. Try to keep watch on the committee's work.
See also: keep, on, watch