I put up a Tent in the garden about a week ago to clean it and get rid of the smell of old plastic. The inner tent has a closed bottom with about 10cm wall around it. Today I was going to pack it up and discovered that the inner tent was full of dead, dried slugs.
I can only assume that they went inside because of the warmth and possibly darkness during the day and could not find their way out again.
This sounds like a good way to kill slugs to me. (A miniature tent should work too.)