4 Answers

Check this>>http://www.wikihow.com/Get-Rid-of-Garden-Slugs

I'm told you can put out a saucer of beer. The snails and slugs are attracted to it and either get drunk and pass out and drown, or simply drown.  Never tried that. 
I purchase a box of slug/snail bait and sprinkle it according to the directions.  I also make a point of getting out to the yard to collect the varmints and the shells as often as possible.  A 4 pound box of the stuff I buy costs about $10 at Orchard Supply Hardware.   

5 ways to get rid of them listed here >> http://www.wikihow.com/Get-Rid-of-Garden-Slugs 

You can put shell grit used for caged birds around your plants. Make it about 4inches wide and about half an inch deep. When snails or slugs try to cross it they scratch their bodies and leave or die there. Untreated sawdust is also good too. It does the same job as shell grit.