Ludi Ludi wrote:
Beer traps work very well. Use the cheapest beer you can find.
You can eat slugs and snails, if you feel like getting revenge! 
The cheapest "beer" is, literally, hooch: the liquid that rises from
sourdough starter.
Very badly-made beer has been compared to hooch, by way of hyperbole, in that both are sour and have a "complex" aroma. Some people have forgotten that hooch is its own substance, with its own history. Genuine hooch is probably even better at attracting slugs, than any commercially-made beer.
If you don't keep sourdough, make some thin flour paste (maybe including some whole wheat), and let that go sour. Much cheaper than beer.
Other ways to control slugs:
Coffee grounds, even used ones, have enough caffeine in them that slugs don't like to crawl over them. Same goes for holly leaves, and any other botanical source of bitter alkaloids.
Copper. (expensive, but it can work)
An overhang that
shelters a surface from rain, smeared with vaseline and sprinkled with salt. Many plastic flowerpots have such an overhang, but this could work on all sorts of barriers, commercial and homemade.
Predator habitat. Slender salamanders have helped my slug situation, ever since my
garden bed has improved enough to sustain them; in other locations, toads or hedgehogs might be better-adapted.
"the qualities of these bacteria, like the heat of the sun, electricity, or the qualities of metals, are part of the storehouse of knowledge of all men. They are manifestations of the laws of nature, free to all men and reserved exclusively to none." SCOTUS, Funk Bros. Seed Co. v. Kale Inoculant Co.