I've been using several products containing iron phosphate over the past five years and I'm sold on this chemical. Not harmful to any other animals, douses their appetite right away and no slimy bodies left around.
The first year, I had to apply it every couple weeks but every year since then there are fewer and fewer slugs and snails. Less product needed. Now I just put it around some of their favorite plants like hosta, marigolds and lettuce and only once or twice.
Both effective and fairly humane.