The four main pests most hosta gardens face are deer, rabbits, voles and slugs/snails.
We've tried most of the common deer deterrant methods...and none of them work....although one of our customers maintains a product called Plant Skydd works well for her. We're convinced that only fencing is effective and that solution is rarely practical. Luckily deer are browsers and generally just take a nip here and a bite there. However, they will occassionally shear a clump. Deer have a definite preference for fragrant hostas...we suspect they're "sweeter." Dogs can also be effective guardians of the hosta patch.
Rabbits can be captured or killed in traps. Generally the only time we have trouble with rabbits is early in the spring when the leaves are just emerging. Once the plants mature we rarely see rabbit damage. Again, the common methods of deterrant (human hair, blood, soap, fox urine, etc.) have not been effective for us.
Voles (and perhaps field mice) are our biggest pest problem. They burrow under the roots and eat not only the fibrous roots but the basal plate as well. Generally, this damage is performed in the winter when the plants are dormant. Most of the plants damaged in this way will live but will be much reduced in size. If you suspect voles, dig the plant and examine the roots. The lack of roots will be obvious and the rodent's teeth marks on the basal plate are frequently visible. Luckily, voles are fairly easily controlled by putting poison seed (which can be obtained in most garden centers) in their holes/burrows. Snakes are also fond of small rodents.
Slugs (and in some parts of the country, snails) eat holes in the hosta leaves and are the most commonly described pest affecting most gardeners. They are also easily controlled by the regular application (about every three weeks) of slug bait which may be obtained at most garden centers. We have not used slug bait at the nursery for about ten years now. We have a small pond which produces lots of toads and frogs and these helpful creatures, in addtion to our wild turkeys, keep the beds slug free. Slugs may be controlled by hand picking as well. A few small flat boards placed strategicallly throughout the garden, but with a little space under each, will attract the slugs since they like to hide. Just look under the boards every couple of days and remove and destroy the slugs. If you're more adventurous you may stalk the garden at night with a flash light and catch the slugs on your hosta plants (generally on the underside of leaves). Some people swear that putting small bowls filled with beer in the garden (buried so that the rim is not an obstacle to the slug) attracts these noxious creatures. They then drown in the bowl. We know this method to be effective....but very messy.
It must be kept in mind that regardless of all the above discussion about pests, hostas are just about the hardiest and most trouble-free plant you can have in your garden.