Corner situation

The corner of garden

OK, so the so called pros came and looked at the corner with the drop where I wanted to put a retaining wall or something. They looked very puzzled and started sucking air through their teeth and I knew they had started the long process of expressing this was something they had no idea how to fix.
Usually this traditional Japanese process starts with tiny signals and escalates gradually. It takes up to 15 minutes with bigger and bigger signs of agony and suffering until you feel sorry for the guy in pain and release him by saying "It's OK, you can go now. Thanks anyway."
However this time there were too many mosquitoes present who were already biting vigorously on the two pro guys (but not on me as I had sprayed myself with deterrent), so the guys' response was more normal human paced.
After a very short discussion between themselves, they told me honestly that this was above their league and I should ask some higher level pros (what they said was "the people who make roads and such") to come and pour some concrete there or something. They also said it would probably be very expensive.
So I decided I would just leave it be. I also briefly though about asking the town hall for support to prevent landslide but the corner is situated in a way that I think they probably won't give a crap.
What I did was to hammer down a couple of long bamboos as posts just on the edge of the drop (not visible in the picture above as the posts are just to the left of where the picture was taken), and filled the gap with branches and soil. It looks nicer now, and if I get some growth there and the soil settles maybe it will behave. I just let it become a mini jungle.   
By the way, the tree I discovered very recently is in the middle of the picture. After I got rid of the weed that had suffocated it, it seems to gain new life. It is a ginkgo tree, with leaves same shape as Tokyo prefecture symbol. This guy can eventually grow up to become a giant, so I better look up.