Today's Idiom - Day 16

not on my watch

When someone says ‘not on my watch”, they mean that they will not allow something to happen while they are in charge, responsible, or on the lookout.
(This expression comes from the military or naval sense of ‘watch’, meaning a period of vigil on land or at sea.)

"I think he intends to leave his caravan in our car park.” “Not on my watch!”