Gather plastic cups, dishes and/or old soda bottles.
Place the cups, dishes and bottles into the garden. Bury cups and dishes to their rims in the soil, but simply remove the lids from soda bottles and place them on their sides.
Fill each cup and dish with the skunky beer. Fill the soda bottle half full of skunky beer, then place it back onto its side in the garden.
Allow the beer traps to sit overnight in your garden, luring slugs in. Slugs are attracted to beer, and once they are inside the traps, they drown.
Empty the traps each morning, refilling them with more skunky beer and placing them back into the garden for the following night.
Increase the amount of slugs repelled by raking up mulch and removing any logs, sticks or other forms of slug shelter in your garden. Keep garden weeds in check to prevent slugs from hiding out in them as well.