“Never let a slug escape!”
Household ammonia at the correct dilution not only destroys slugs, at the 5:1 dilution the solution it actually provides a source of nitrogen which plants absorb through their foliage. It is effective at killing baby slugs early in the spring as plant growth is emerging. Spray it on the emerging plant and on the soil around it. It is also effective on larger slugs in midsummer, as long as the ammonia is sprayed on the slug.
Mix 1 part household ammonia with 5 parts of water – for a total of 6 parts. (Example: mix 1 cup of ammonia with 5 cups water, for a total of 6 cups.) Some like to use a squirt of liquid dish soap to help the ammonia stay in contact with the slug, or use a “spreader/sticker” product. You’ll need to use some sort of a sprayer – either a garden type or an old Windex-type bottle.
NOTE: You can make the solution weaker if you like.