The recipe that saved my garden (and resulted from far too much reading about what does what to a slug!)
In a medium/large spray bottle mix the following:
about 1/4 to 1/2 inch layer of regular table salt
about a cup of cold brewed coffee (I just used what was left in the pot after we'd had it in the morning)
about a tablespoon of all purpose cleaner (I used Wilkinson's version of Lemon Flash)
fill to the top with tap water
shake to mix.
Spray on the little plant-eating bastards!
(I tried one version with lots of salt and a bunch of instant coffee granules. It was way too strong and burnt the top of my lawn. If you have big slugs, you might want to veer towards a bit more salt in the mixture.)
I went out at the end of the day for a few days in a row and paid particular attention to the baby slugs (little white things about an inch long that seem to love crawling around in the grass). This stuff dissolves them and leaves a tiny white mark on your grass where it used to be.
For the bigger ones, you will have to spray them til they're soaked. The end up shriveling a bit, falling over on their side, and dying. My experience has been that these either get picked up by birds (which is why you want to keep the soap level low) and beetles, or they shrivel in the sun to absolutely nothing.
After a few days of vigilant spraying (going out a few times a night, and if it was chilly in the morning, then as well), I now have almost no slugs. I think I've seen one in the past few days, even with the wet weather. Before, I would have seen about 50 babies and 20 adults.