Hey, I am pretty serious about trekking the length of the great wall. I have found a bunch of people who have done it and it seems doable with a fair bit of planning in advance. I dont think I would have any problem with the mapping and routes, but I have heard you  need to get permission from the Govt. to trek on certain parts of the wall. Would anyone know who I would need to approach in order to do that? Thanks alot.