Will stood upon his guard, and scrutinised this figure from head to foot.

I had never thought of it before, but I now resolved to be upon my guard.

I was therefore obliged, on all occasions, to be upon my guard.

Yet the old man gets up and stands upon his guard, and will know of them what they are.

What his purpose may be my friend does not know, but he warns us to be upon our guard.

"I thank you for that," said I, pretty close upon my guard.

Go then, with my blessing, but stay upon your guard.

She had about her a watchful look, as of one who is upon her guard.

But in the meantime we must be upon our guard!

And we've got to be pretty much upon our guard from now on.