You can use the scratchiness of silicon carbide sandpaper to discourage slugs in your raised bed garden.
After numerous years of battling with slugs feeding on my garden foliage, I became obsessed with finding a permanent way to defeat them. My persistence eventually paid off when I began concentrating on the “scratchiness” approach. Here’s how it works. (Note: This method requires raised beds.)
First, purchase a common hardware product known as silicon carbide. Its purpose is to sand drywall spackle, and it comes in boxes of 50 sheets — 4 1⁄4 inches wide by 11 1⁄4 inches long — in 80 grit. You’ll also need a box of stainless steel staples and a staple gun. Now, cut the sheets in half lengthwise using a utility knife, then staple them end-to-end to the uppermost sides of your raised beds.
Make sure you purchase silicon carbide sheets that are waterproof — some types are and some aren’t. When applying these sheets, be certain to staple them tightly against the raised bed frames: Do not leave any gaps for slugs to crawl “under” these barrier sheets.
This method has worked magically for me, and I can honestly say not a single slug has crossed these barriers! To make a good thing even better, I only have to replace the silicon carbide sheets every four years.