on guard

phr

• ① 在站岗;在守望;警戒着
  • Who's on guard?谁在站岗?
  • put [set] a person on his guard使某人提防[当心]<against>
  • He's constantly on guard against any danger.他时时刻刻在提防危险。
  • Be on your guard against pickpockets [thieves].谨防扒手[小偷]。