He escaped by passing himself off as a guard.

他伪装成看守人而得以脱逃。

《牛津词典》

The lawyer's apparently innocent question was designed to catch the witness off (his) guard.

律师看似不经意的问题是为了使证人措手不及。

《牛津词典》

He had a way of throwing Helen off guard with his charm when she least expected it.

他有办法用他的魅力让海伦在最意想不到的时候失去戒备。

《柯林斯英汉双解大词典》

Iowa National Guard veteran Kyle Hoefling took off from work to join a rally the night before Mr.Obama's visit.

VOA: standard.2010.03.25

At least since the eighteenth century, these lines have been singled out for their beauty and, considering that Milton is describing the hideous demons under Satan's control, the pastoral elegance of this little simile really catches us off guard.

至少从19世纪起，这些句子因为它们的美感经常被单列出来，并被认为是弥尔顿在描述撒旦控制下的可怕的恶魔,这个小比喻诗歌上的优雅,确实使我们毫无防备。

耶鲁公开课 - 弥尔顿课程节选

(NO TRANSCRIPTS) The intensity of the quake, which rocked the city for more than a minute, caught many off guard.

VOA: standard.2009.09.07

My point was that the mayor of New York had forgotten about an attack that happened in New York during that administration, and I was caught off guard by that fact, as I think anybody that might have been watching was sort of caught off guard by what he was saying and what he meant to say.

WHITEHOUSE: Press Briefing

Two months later an Italian coast guard boat off Naples came across a remarkable scene.

FORBES: Companies, People, Ideas

Seventeen Haitian migrants -- all male -- were questioned Thursday aboard the freighter the Coast Guard stopped off Miami after its captain reported the vessel had been hijacked.

CNN: Haitians flee to U.S. in boats