While ducks are the best solution to the slug problem (a seriously big one after yet another mild winter), they're not practical unless you have a large garden free from marauding cats and foxes. In my experience the only entirely organic method guaranteed to work is to go out after dark with a torch and hunt them. I snip them in two with a stainless steel scissors (you soon lose your squeamishness), other gardeners collect them into a bucket of salt water or bleach (but then you have to dispose of it carefully).
Beer traps (containers of lager sunk into the ground) are expensive, but are useful for protecting specific areas such as greenhouses or small beds. Slug pellets, if you choose them, should be used very sparingly, not in heaps or thickly sprinkled. And, because they actually attract slugs, don't put them right next to the plants you want to protect.