Did you get my PM? My answer was similar to Chan's--seastacks are big enough to form rough boundaries and walls, and other rocks are diverse enough that you could use them for more detailed areas. Also, Chan's sandbags would be great for an aesthetic flair in certain parts of the map. As for your comment elsewhere on how to "snipe" people if they try to leave the trenches, a hard kill Zone, with the bottom placed slightly above the tops of the rocks, would do the trick. If you wanna be nice, give them a soft kill zone a foot or two down, so they have the warning that at least they shouldn't be going up there.