Various methods of using copper as a barrier were considered, lengths of copper wire stapled to the sides of the garden box (too narrow to really stop a hungry slug), copper pipe strap nailed to the box (too expensive for an experiment) and strips of copper mesh (available in decent lengths for a reasonable price, but not readily to hand) While poking through the kitchen section of Home Hardware I found copper scourers. They seemed to be made of copper mesh rolled into a donut.
I bought a package -- and was gently admonished by the cashier (and the label) not to use them on non-stick pans -- and headed home.
The scourers were unrolled and gave me two tubular lengths of copper mesh which I cut apart into lengths of 'tape' which I stapled around the base of the garden box which we planted today.
I will report later on the effectiveness of the wire obstacle we've erected to keep the slugs out of our garden box. Once we've had a chance to see how well they work, that is. Even if they don't care about the copper, they'll probably have a pretty rotten time trying to get across the sharp metal mesh.