In the morning you can crush them where they're hiding by whacking the board on the ground. Slugs are attracted to beer, and will crawl into the cans and drown. Mix 1 teaspoon of the yeast and 1 tablespoon sugar into 1 cup water. Stir or shake until the yeast and sugar have dissolved, then place the liquid in a shallow pan or commercial slug traps. Commercial traps have lids that prevent rain from diluting the solution.
Check traps frequently for slugs hiding under and around the base or lid.
There are also a variety of manufactured snail traps available, including a plastic model that you press into the soil. Then you add water and a mix that's mostly cornstarch, barley, yeast, and sucrose.