It comes in 15-foot rolls, usually under the brand name of Corry’s Slug and Snail Barrier Tape and costs about $10. The interesting thing about copper is that it generates an electrical reaction when slugs or snails try to slither across it. And they don’t like that one bit! It makes them backtrack, which is great.
I think the tape would be too expensive to completely surround a raised bed planting, for example, but I have made rings and placed them on the soil around kale plants and it worked great. Just make sure there aren’t any leaves hanging down onto the soil surface because that would be another way for a slug to climb up into a plant!
By the way, it’s not technically “tape,” but rather a paper-backed copper substance.
You can find the rolls of tape at garden centers, hardware stores and online.