[ted]

All these ideas are wrong - though I do like the shotgun idea conceptually - because you are only making the problem worse by killing the slugs you have. But the answer I'm going to give you - and this IS the answer to slugs - is not something you will believe, and it sounds really really crazy. But it works, and it's the only thing that works. Take it from a Northwest gardener.
The mistake is to think you accomplish anything by killing the slugs. Slugs, believe it or not, are territorial. If slugs are invading your crop from the areas around it, and you kill them, their territory is taken up by slugs just beyond it. You have to go on and on killing the new residents; it will be as if you are 'wicking' all the slugs in to your garden. The answer -
Here's where it gets hard, so hang on -
is to train the slugs you've got.

Stop laughing. It works. Go to your crop with a jar, unless you are not squeamish about handling the slimey buggers. Put them, one at a time, in the jar or cup them in your hands. Now scream at them. Swear at them. Call them every name you can think of. I know, I know. Weird, but true. Shake them, scream at them, but don't kill them.
Then put them somewhere close by that you don't mind them being, close enough that they can find their home territory. They won't come back to the place from which they were 'abducted by aliens!'

Believe me, I know how insane this sounds. I also know that your neighbors will give you long, suspicious looks, and will avoid you at the grocery store, but there you are, life is hard. I also know this works. The local slugs love strawberries, but in my garden, I only have to abuse the slugs for maybe a week early in the year, and a few times through the harvest season, and they can munch on things *right next to* the berries but will leave the berries absolutely alone.

And, yes, I am crazy, but that's beside the point. This works, and it's the only thing that works. The nearby territories are maintained by the slugs you've trained, and except for one or two newcomers, you won't have to worry about slugs any more. (For ranchers: this is the answer to cougars and wolves, too, but you need a really big jar, and don't be close when you let them go again, cuz they come out really pissed.) For slugs, it's dead easy. Give it a try!