If I'm not mistaken, a wire won't do the trick. It needs to be a strip
wide
enough that the entire body must pass over it at once to be effective.

I'd rather just kill them, though...

We bought copper flashing at HD today. I'd rather kill them, too, but I
don't want to find out I have them by waking up to shredded leaves or
partially eaten flowers! So we're going the two pronged way: bait and
copper.

Diana