I have an old kitchen knife which is known as the slug murdering knife, although I do use if for other things in the garden as well.
For a moment I thought you were going to say.........'though I do use it for other things in the
kitchen....'
Being quite primitive creatures, I'm not sure just how immediately chopping in half kills slugs. Standing on them against a concrete path, and twisting about, as long as you don't have deep treads on your boots, obliterates them, then other mini critters come along and clear up. I've never had hens or ducks that would eat slugs - fusspots don't like the slime I suppose.