Slugs must be able to get into the raised bed or container. A simple way to prevent this is to place copper tape or wire or tubing around the perimeter of the raised bed or container. It can be a decorative element just make sure it goes around the entire perimeter. Fasten it down securely. The slug slime interacts with the copper essentially electrocuting the slug. If your plants are in traditional beds, place the copper wire or even copper pennies around the base of the plant to protect them.
Beer has long been a remedy for slugs but use cheap, fresh beer instead of stale beer. This method will confirm the damage is actually being done by slugs as well. At dusk, pour about 2" of beer into a sour cream or margarine container. I like the smaller cream cheese containers for this purpose. Bury the container to the rim near the damaged plants. The next morning remove the drunken slugs and dump the debris nearby. This will attract natural slug predators effectively giving two lines of defence against the slimy little critters.
Caffeine is an effective slug control. Pour left-over coffee into a spray bottle then spray directly onto slugs in the evening. Place used coffee grinds around the slug damaged plants. If you are dealing with a situation like a strawberry patch such as mine that is not planted in rows, sprinkle used coffee grinds in and around the plants. Vinegar sprayed on slugs will act much the same way however it is an herbicide so don't spray it on plants or where the over spray will get onto plants.
Iron phosphate sold under brand names like Sluggo work to eradicate slugs without poisons. However, I do not recommend them. My first experience with iron phosphate was when I was just starting a vegetable garden in another house. At that time we had ponds and welcomed toad and frogs as well. We had a lovely fat toad who mysteriously disappeared after using this product. For the rest of that season we had no toads and we fished several birds out of the ponds. So I will not use this product despite the labelling that says it is safe. Now this is just based on my experience but there is evidence that slug pellets are reducing the natural slug predators.
Diatomaceous earth is the mined fossilized remains of dinosaur-era, sea-going creatures called diatoms. On a microscopic level it is incredibly sharp causing cuts on the slugs as they travel over it. The cuts cause the slugs to dehydrate on contact. It is best used around plants that are being damaged by slugs and refreshen after a rain or watering. Diatomaceous earth is a fine powder so a dust mask should be used during application. This is not a solution I would recommend to anyone with respiratory problems since you will be working in and around the plants while the diatomaceous earth is present.
Attracting natural predators for slugs is one of the easiest ways to control them. Natural predators include: frogs, song thrushes, mistle thrushes, redwing blackbirds, ground beetles, Bacillius Thurungiensis, centipedes, fire flies and many birds. Duck and chickens like slugs as well and if you've read this blog you will see I have welcomed my guinea hen visitor because of the insect control. When encouraging natural predators do not use pesticides!
As pests go, slugs are fairly easy to identify either from their dried slime trails or direct spotting. So get out there and slug those slugs!