"Leave No Trace Fly" White gouache on tree bark - I spent the last week at Boy Scout Summer camp with my youngest Son. I am one of the Assistant Scout Masters for his troop. I was going to use my knife to carve the fly into the bark, but that would permanently scar the tree and would be against the "Leave No Trace" policy we try to teach the kids. So instead, I pulled out my white water soluble gouache and painted the fly on the tree. It rained a couple of times during our stay and all traces of the fly are now gone.