Slimy, slobbery, slithering, slippery slugs: Your garden might play host to these disgusting creatures without you even knowing it because slugs are nocturnal, sliding beneath the cool, moist shelter of rocks and leaving by day.
Holes chomped into leaves and fruits are telltale signs of slug feeding. A more certain sign of slug activity is the silvery trail of dried mucous that these pests leave in their wake. If that's not sufficiently convincing, go out into the garden at night with a flashlight and surprise them.
Right then and there is when you can put an end to your slugs, or to at least some of them. Stomp on them, squish them, or drop them into salty or soapy water. Still, hand-picking is limited in its effectiveness. Slugs are sluggish, but a single slug can travel 30 feet or more in a night, so new slugs could keep moving in.
Moist, shady spots are needed for egg-laying, and even the adults like this sort of environment. You could make the environment less hospitable to slugs by cleaning up debris and mulch, and by promoting drier conditions by weeding and thinning excess plants. The problem is that, like slugs, most garden plants enjoy mulch and moist soil; so a more active attack is usually warranted.
Keeping poultry near or in your garden will take their toll on slugs, as will encouraging toads.
You might try keeping slugs at bay by laying down a 3-inch-wide strip of dry wood ashes, fine sawdust or diatomaceous earth. Unfortunately, wetting decreases the effectiveness of any of these materials - and wet conditions are when slugs become most active. Also effective, as long as there are no leaf or stem bridges, is copper, either a strip or a screen, which gives slugs a mild shock when they make contact with it.
Rather than keeping slugs at bay, you could actively attract slugs. No need to invest in poison baits, though. Grapefruit halves, boards or upside-down flower pots all make cozy nooks into which slugs can crawl by day. Inspect traps first thing in the morning, then crush the slugs.
A "slug tavern" attracts slugs with beer. This trap can be as simple as a shallow saucer filled with beer, or as elaborate as a covered coffee can sunk into the ground up to the level of entry holes cut in its side.