There's no silver bullet for getting rid of slugs.
You need to combine the classic Integrated Pest Management [IPM] techniques of cultural, mechanical, and chemical controls. Does that sound too academic? It's actually very practical. And some of it involves wearing your bathrobe in your garden! Watch Tricia control slugs with the full range of organic methods.
Monitor on night patrol
Hang out in your garden and look for unwanted visitors -- at night, as well as in the daytime. When the sun's out, look for the silvery trails of slugs. When the moon's out, get your flashlight and go on a slug hunt. In the great garden cycle of life and death, slugs are a tasty treat for any backyard chickens you know.
Remove the welcome mat
Back in daylight, close up happy hiding places when you take away scraps of wood or cardboard, clean out weeds and debris, and pull up all that ivy (rats love to nest in ivy, too) and other dense groundcovers.
Get into drip irrigation
Yes, one more reason to install drip irrigation. Slugs don't want to cruise over dry soil, they want damp slickness. Overhead watering creates the moist surfaces that make life go so very smoothly for slugs.
Get rough, and grow plants slugs hate
Make things rough for slugs instead. If you got around on a delicate, slimy foot you wouldn't want to travel over shredded cedar bark or cocoa shells. Sprinkle sharp-edged Safer Ant & Crawling Insect Killer around plants to thwart the slugs' progress; this product is labeled for slug control and contains diatomaceous earth along with bait. Leaves can be rough too, and slugs really don't want to move across rosemary, lavender, California poppies, and nasturtiums.
Slug traps, and bait that won't harm pets
You can deploy copper wire labeled for slug control. The copper reacts with the slug mucus and causes disruption to the slug's nervous system, similar to the slug being electrocuted. Want to be non-violent and put up a slug fence? Reminiscent of the popular fairy gardens, you can make a tiny slug fence out of window screen, sink one edge into the soil, and leave the other edge 4" above ground level.
The trick here is that slug mucus oozes through the mesh of the screen and the slugs run out of traction as they attempt to climb their way into your vegetable patch. A simple trap is a 6" piece of smooth wood or cardboard. The slugs will enjoy hiding there, so flip this every few days to find slugs. If you want to chemically kill the slugs (but not your pets or the other wildlife) with iron phosphate, scatter around Sluggo granules or the other Sluggo products -- all are labeled for slug control. There are lots of slugs in your garden, and you'll need to use lots of techniques to deal with them.
Strap on your head lamp tonight, and get started on a variety of methods for organic slug control.