I had a wacky idea for discouraging slugs in a raised bed ... I haven't even tried it yet.
I was thinking of putting a low hoop tunnel over the bed when winter gets warm enough that the plastic would thaw the bed and wake up any slugs. Maybe put beer saucers and some iron phosphate slug bait in the bed.
After giving the slugs a week or so to thaw and wake and drown, I would take the plastic away and let it freeze solid again, hopefully killing more slugs.
However, even if this turned out to be very effective, all it would do is create one small slug-free hole in the middle of your neighborhood. That would give you one, maybe two days of slug-less-ness before enough slugs wandered in from next door to make the effort futile.
