You don't have a snail problem, you have a duck deficiency!
~ Bill Mollison, author of Permaculture Design Manual

Keeping animals on your property provides a complete nutrient cycle of a farm or small acreage. They can control pests and vegetation by careful planning and management of their forage.
Even a simple worm farm keep in a garage or cupboard in a home unit is highly beneficial in managing organic waste (kitchen scraps) and turning this into a superb garden fertiliser (and saves our overburdened rubbish tips).
Uses of animals include:
High quality manures for garden fertiliser.
Soil turning (particularly pigs and chickens), weeding and depositing essential manures into the soil.
  Providing an income; meat, milk & eggs for the meal table
  And are great pets!

Best Buy: Chicken Tractor: The Permaculture Guide to Happy Hens and Healthy Soil
by Andy Lee, Pat Foreman  Paperback (1998)