The most modern approach, but also the most expensive, is to use slug parasites such as Nemaslug, which are parasitic eelworms (nematodes). Mix them with water and simply apply to the soil with a watering can. They destroy the slugs underground, where much of the damage takes place, and attack no other creatures. This certainly works, especially in summer but it's less effective on clay soils and is expensive. (Slug Stoppa and Nemaslug are available from the Organic Gardening Catalogue, 01932 248541).