on watch

on (one's) watch

Under one's supervision; while one is in a position of power, authority, or responsibility. I can't believe you let this happen on your watch. It's strange—even though it wasn't on my watch, I still feel partly responsible for the robbery.
See also: on, watch
Farlex Dictionary of Idioms.

on someone's watch

while someone is on duty; while someone is supposed to be in charge of a situation. I am not responsible since it didn't happen on my watch. I guess I have to bear the blame since it happened on my watch.
See also: on, watch
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • at (one's) doorstep
  • at doorstep
  • at expense
  • at somebody's expense
  • at someone's expense
  • at (one's) expense
  • at door
  • at (one's) door
  • at one's door
  • a ball and chain