There are pellets available called "Escar-Go" which are basically iron pellets wrapped in slug bait. A high concentration of iron is fatal to slugs, but doesn't harm the soil or most other animals.
Also, slugs seem to be repelled by caffinated products. Adding coffee grounds to the soil in your garden should discourage the slugs from hanging around and will also add nutrients to the soil.
Third tip, slugs are allergic to copper. This one, as I understand it, is as much "fun" as salt (which I tend not to use, because I consider it inhumane). I'm told they even "spark", but I'm not sure if that's figurative or literal.
Speaking of salt, it's not a good idea to use it in the garden, because it's not too good for the plants and the effect tends to linger long after the salt itself has been "washed away".