Really nice. I keep trying to give my insights to others abt what makes dios fail, but this sez how to do it right better than words. Really creative, straightforward, entirely plausible (oh, why not!!), and lets you use your imagination to fill in the rest.
I guess my only comment would be that along the lines of the bottom of the trench, what if you did the retaining wall with some tech looking stuff like, oh I don't know, computer fan mesh or steel wool, or Future sprayed from that thing on his wrist, or ...
Very well done!