I'm trying to stick to organic remedies, if possible. It's my understanding that snails/slugs will not cross over the lava rock because of its sharp edges, similar to diatomaceous earth. The benefit of the rock would be that it won't wash away, and might even look halfway decent. I could pick it up at the season's end, and use it again the following season. For now, I'll go with Sluggo, but the lava rock remedy seems better to me, if it really works.
Maybe Pepper-Guru will weigh in. I'd like his take on it.