A little bit of swing-set style chain, a bicycle inner-tube and a conduit clip, which fastens around the surge protector's wire/cable and are available in the electrical aisle. You could use one-way head screws to bolt it together if you wanted an added measure of security above a regular bolt head. Instead of the conduit clamp, a couple of "two-hole straps" (sized appropriately for the surge protector's cable) bolted together around the surge protector's cable would work, too. Having a mooring point for the chain on the surge protector allows maximum flexibility for securing it to available objects. If nothing else, it has a fair intimidation factor, so, hopefully, the would-be Artful Dodger moves on to an easier target.
Usually, the pad lock through the power pedestal's metal clips works fine, but sometimes the clips are boogered up. It's not worth making an insurance claim for a 200 dollar item. It's easier to lock it and look like I don't trust people, which is fine with me. If someone takes offense, they'll just have to get over it.

