Cut entry holes into the container above ground level. Slugs like fresh beer so replenish the trap frequently. Wood ashes, diatomaceous earth, cedar wood chips, cinders, and copper strips or screening can ail be effective barriers against snails. Wood ashes and diatomaceous earth are only effective when dry. Cinders remain effective when wet.
Salt does kill slugs and snails but repeated use can make the soil toxic to plants.
Copper barriers are effective against both slugs and snails. Slug and snail slime apparently interacts with the copper to produce an electric shock. Copper was more than 95 percent effective when the top edge of the strip was bent down to form a flange. Copper strips or screening can easily be attached to raised wooden beds. The top should be bent over forming a flange.