Mini Construction Upadate Type Thing:
I was there t'other day and took a couple of pics of how they're diddlin'. Excuse the quality of the photos, I took them on my phone, so I know you can't see a lot of detail.
Also, what you cannot see is: Behind the trees on the right in the first picture and on the left in the second, there seems to be a massive amount of steelwork (steel mesh cages that goes in the concrete footers) already in the ground. HOWEVER, you are only able to see this while riding samurai, as such, I am unaware of exactly how "in the ground" they were, they may very well have been "on the ground"