I did a search. The guy's channel is Off Grid Build. Looks like he hasn't posted anything in 7 months. He was doing regular videos, but I guess life happened. So, I don't know if he went through with using the rocks for raised beds. I think I made the comment on one of his videos from 2 years ago. Being in NY, he might have more slugs than you do.

https://www.youtube.com/user/offthegridbuild

Anyway, I always thought that if you have the rocks lying around, it would be a better method than using wood.