Here are a few traditional markers constructed with rocks. Note that the "turn" markers are constructed so that the smaller rock on the ground points in the direction of the trail.
This is the Trail
Trail turns left
Trail turns right
Danger ahead
Other traditional markers include broken tree branches pointed in the direction the follower is supposed to go. You can also use sticks on the ground to make arrows. Breaking tree branches may not be appropriate in some areas but if breaking the branch helps keep the trail clear it is usually acceptable.