on guard on one's guard upon one's guard on your guard
on_guard%5:00:00:wary:00 on_one's_guard%5:00:00:wary:00 upon_one's_guard%5:00:00:wary:00 on_your_guard%5:00:00:wary:00
vigilant
on guard against con artists must remain on your guard in such a situation