put on guard

Here in Poland, even the younger generation are being put on guard.

If it caused a great many men to be put on guard — and hence more respectful in their dealings with female colleagues — that’s all to the good.

Nations can be put on guard and personnel dispatched to the bread line with a presidential tweet.

A raw Highlander from a northern depot was put on guard at the C.O.'s tent.

After they had relieved the Company in the trenches, Lloyd, with two of the old company men, was put on guard in one of the traverses.