line of defense
line of defence

You are the real line of defense, and your behavior.

But those two were, for the moment, the only line of defense.

But West thought he had a sure set with his line of defense.

You'll be the last line of defense for whatever comes.

Being a teacher, we're in the first line of defense.

It is the first line of defense for the nation.

Until he found something better, it was his first line of defense.

And, as that other saying goes, you are the first line of defense.

That was the first line of defense, if things went wrong.

And certainly your hard drive is the front line of defense there.