Ducks rock! Nothing better for slug control. I couldn't have a garden without them. We in the Pacific NW are the mother country of all slugs, I think.
However, they will tromple all your plants. So for next year, here's your game plan: Fence them IN your garden before you plant to de-slug the area, for as long as you can/like. Then when you are ready to plant, fence them OUT. You may free-range them (I do) or have an outer circle of fence (like a dry moat, so to speak) for them to patrol.
They are the easiest animal to keep. They keep themselves. And their eggs are rich and delish.