[math-fun] Finding other people

The recent discussion of giving directions to people who don't know where they are reminded me of a problem that I think is original with me. Suppose a large number of people are placed randomly in an immense forest. There are no landmarks, the ground is level, and it's always heavily overcast so there's no way to tell which way is north. You can leave marks. People and marks can be seen iff you get within 10 meters of them. If everyone knows the above before they're transported to the forest, so they can discuss the problem with the others, what would be a good strategy? There isn't necessarily one best answer. But some answers are better than others.