Copper, diatomaceous earth, beer traps, sand, or slug bait are all viable options. If it's bad and the plants are small, I myself would do the bait. Are you sure it's slug damage?

Kevin

Beer traps with one in close proximity to every seedling. The bait works but involves chemicals and a bit more expensive. Plus you get to drink the rest of the beer! I give my slugs a nice triple IPA every spring.

"I give my slugs a nice triple IPA every morning."

Fixed it for you.