Electric Fence for the Greenhouse ?

I was out tidying up the Space Saver greenhouse this morning at 7am and ended up moving the Catawissa Walking Onions down a level as some had just started to touch the trays on the shelf above them.

It looks as if I really need to get the greenhouse on Mill Green Allotment clear  and more importantly slug and snail free as I found one of each this morning on the Space Saver in the back garden.

I'm thinking of setting up an electric fence with copper wire and a 9v battery at the entrance to stop the blighters getting in there in the first place.