Hostas are especially vulnerable in spring, when the leaves are rolled around themselves and a mollusc can eat through several layers.
If you use slug pellets, be sure to apply them in March and April, when the hostas are beginning to nudge their noses through the soil. A new organic pellet, Ferramol, is not hazardous to other wildlife or pets, and it breaks down harmlessly (from Fruit Hill Farm: 027-50710; www.fruithillfarm.com). All slug pellets should be used sparingly. Barriers of different materials are effective to varying degrees in different gardens. All of the following have given some protection in my garden: ashes, coffee grounds, hair clippings, dried and crushed egg shells, dried grass cuttings, grit.
Slugs and snails may also be lured into beer traps. Or you can trap them under wet newspaper, slates or planks of wood. Or (and here's the disgusting bit, so move onto the next paragraph if you're squeamish), you can hunt them by torchlight after dark, and quickly snip them in half with a scissors.
Don't water hostas at night, as this creates a moist environment, which is exactly what molluscs like. In very snaily and sluggy gardens, the only way to grow hostas is in containers: girdle them with copper tape or a slick of petroleum jelly.
Or take advantage of the fact that slugs and snails can't swim, and stand the pots in containers of water, raising them over the water's surface on pot feet or other supports, to avoid the compost becoming sodden. Make sure the leaves aren't touching other plants or surfaces, as resourceful marauders will use these as bridges.