There's a nice but rarely found predator slug: Limax maximus (German: Tigerschnegel, english: leopard slug, http://en.wikipedia.org/wiki/Limax_maximus )
Amazing! I read this yesterday afternoon, and then yesterday evening I was checking for slugs, and I ran into one of these leopard slugs! Luckily I already knew these slugs are beneficial and so didn't kill it. It did seem, though, as though it had received a shock from the electric fence, as it was sitting below it without moving.
My wife wanted me to put it in our fenced garden, but I was afraid it would try to get out as it doesn't have that much space to hide in there, but wouldn't be able because of the 9V fence. So I put it in my daughter's strawberry garden, where there's loads of big and small slugs.
Anyway, the fence seems to have done the job well enough while we were away. There was only one semi-big brown slug I could find, but still loads of small, white ones (two of them mating, so that explains it) drilling holes in the large cabbage leaves. We'll keep picking those by hand, and maybe sprinkle a few of those slug pellets under the planks. Everything is well under control now.
I now have to add a small LED lamp to the set-up that functions as a resistance (which is better for the batteries) and shows me when there is a short-circuit (right now I check if the wet-up is still working by putting my tongue to the two wires, much to my wife's amusement). It rained a lot while we were away and the burn marks behind the metal wires are a sign that there was quite a bit of short-circuiting due to water drops. Maybe I'll have to add a small cover to protect the wires from rain drops.
I'm also contemplating moving to 7.2V or even 4.8V (6 or 4 batteries respectively), as the 9V is frying the (smaller) slugs and of course, small is beautiful.
Some of the plants are coming along nicely, now that we finally have some really good weather, but other problems are popping up (lice, etc), and so we're learning a lot. One discouraging thing is that our berry plants are doing really well, but are hardly carrying any berries! I don't think it was a frost, but winds were blowing quite hard when they were flowering. Or maybe we just didn't add enough compost back in March...
So no berries this year...