Where I live, some years have ten times as many slugs as other years. When they are "in season", they can eat almost anything right down to the ground.
Other years, they merely kill every Delphinium seedling I put on the deck.
You might accept the damage most years, and then if things get bad, use a trap crop and try to draw them away from certain beds using beer saucers elsewhere ...
... or consider non-toxic ways reducing their numbers if things get TOO bad. I think that's the core of "Integrated Pest Management" - escalate your response only enough to make the damage bearable.
There is no way to "kill them all off", because they migrate freely from neighbors' yards.
You might consider a higher level of protection for young seedlings, especially if you're hardening them off when there is not much else for slugs to eat. I lost 100% of several trays of Delphiniums until I realized that it was not ME that was killing them. Like, putting them up on a table and covering the table legs with a ring of copper tape.
