seaming berber carpet
If the carpet is in a doorway or something, you could always nail down a piece of naplock and bend it down over the carpet, too.
HomeDepot: I don't think he wants to hot melt tape a seam in the carpet. I think he just has a cut edge on his carpet, and he wants to prevent it from raveling. I'm not sure about this, but since Kanga-back carpets are normally glued down (and not hot taped) then maybe the tufts are glued in so that they wouldn't ravel anyhow, even if you didn't do anything to prevent ravelling. If the tufts are glued in, rather than woven in, then if the tufts come loose from that glue, then it would be individual tufts that would come off the edge, but the carpet wouldn't "unravel" at all.