>>Why not try rubbing some earth to form an outline.I have used peat a few times on Dartmoor and it worked a treat,and washes off with the first rain.<<

So earth and peat are of, because they are natural is OK but Calcium Carbonate is unnatural so totally bad?
So a bit of chalk rock would be OK but not the same thing purified and shaped into sticks.
Methinks there is a bit of double standards there.

The most damaging stuff I have seen is a cup filled with sheep droppings. Stong stuff is Sh*t