Slugs: How to repel, perhaps kill, slugs with coffee (caffeine)
Easy to do, inexpensive, and safe. ....almost too good to be true....
Scroll down to "Do the java-jive against slugs," more than halfway down the page.
Now, instead of pouring left-over coffee down the sink, save it and pour it over the soil around plants that need protection. Slugs will avoid the area (according to Owen, whose source is the USDA, Hawaii).
Or put down used coffee grounds for similar results. (Used coffee grounds can be had for free at many Starbucks. Suggestion: Keep heavy-duty garbage bags in your car, or a tub, 'cause sometimes there's seepage from the grounds.)
Here is a link that might be useful: By Marion Owen: Learn how coffee can help you fight the war on slime