on one's guard

Related to on one's guard: warship

on (one's) guard

Especially careful or vigilant; prepared for danger or surprises. He's got a lot of tricky moves, so be on your guard! Those trails can be a bit treacherous to climb. I just hope she's on her guard.
See also: guard, on
Farlex Dictionary of Idioms.

on one's guard

see under off guard.
See also: guard, on
The American Heritage® Dictionary of Idioms by Christine Ammer.
See also:
  • on (one's) guard
  • on guard
  • on your guard
  • always be on (one's) guard
  • off (one's) guard
  • off guard
  • off your guard
  • catch (one) off (one's) guard
  • catch (one) off guard
  • catch off guard