Slug Resistant Plants
If you do not want to kill slugs but you do not want them eating your garden either, why not fill your garden with plants that are slug resistant?
If a plant becomes squashy and slimy when it dies then slugs will probably want to eat them. Slug resistant plants can simply be plants that slugs don't like eating. These include plants with woody branches and evergreen leaves. Some might withstand a slug attack simply because they grow faster than they can be eaten or contain sap that slugs don't like.
The following is a list of plants that would likely survive a slug invasion. Google them to see what they look like if you are unsure.
Saxifraga x urbium
Anemone x hybrida