I am attempting to build a privacy fence that will sit just behind a retaining wall (as in, on the ground behind the wall and not on the wall itself).
While digging today I realized that while the ground behind the retaining wall does have ~10" of soil on top, underneath the thin layer of soil seems to be gravel.
I assume that the retaining wall looks almost exactly like this underneath https://i.stack.imgur.com/1dgWc.jpg.
The good news is I only need to set two posts into this gravel, but I am a bit of a loss on how to create the hole for the post. A few questions for anyone who may have some knowledgeable advice
First and foremost, will setting two posts in concrete behind this wall create any structural risk to the wall?
How should I dig 2 foots deep holes into straight gravel? Will a rented auger even work through it? Will a post hole digger and a digging bar work any better?
Thanks in advance!