Hi All,
Well the Slug fence was successful! One problem was that the copper soon got tarnished, even though most mornings I'd use a toothbrush for bodies, and soil that was on the track. Next time I would have a vertical wall with the track on the outer side, and perhaps, if I can find some scrap stainless steel, this might be better. Also make it an inverted L so that the rain stays off it. As for the complicated circuit I was looking for, the simple 12V battery with little solar panel, was maintenance free all summer, and even though many slugs etc must have turned back, some got halfway across before the slime cleaned the track enough for some current, then it was too late.
Hope this is of interest, Cheers, Camerart.