Rek'sai unbreakable tunnel on Crystal Scar

Cant get a picture right now (when i can ill edit), but if you place a tunnel on a certain place on crystal scar, it is i possible to break. It also has an unlimited time limit. To recreate this, follow these short steps. 1) Go into tribush 2) You will be tunneling through the terrain above tribush 3)T unnel up on a small angle so that you almost go through the full length of it; Once youve done this, if done properly, you have a fully unbreakable tunnel. I will edit with a picture once able to get back on my computer!

[EDIT] Here is where it has to be placed http://i.imgur.com/pVMy8G7.jpg