Good idea. I just assumed people would realise that all that stuff meant no shelter and that was the idea of it.
ninja: Maybe a rule like " You must never stay for more than 2 mintues in a place that no enemy mob can reach. "
No shelters of any kind, no blockades of any kind, no camping in a place unreachable by monsters, no lighting greater than a small area, no hiding in the ocean overnight(lol). No staying on small islands.
I would just say no shelters of any kind, if people want to eliminate the difficulty of your challenge by finding loop holes, that is their own problem, would kind of defeat the point though.