Double rod mesh including privacy screen on L-stones! Feasible?

Frost depth depends on how frost-sensitive the soil is. With our clay, we are probably around one meter. However, a fence post does not necessarily have to be completely frost-proof. And at the latest, when you reach solid rock, you can stop.

It is not just about frost. The foundation must bear the torque that your fence transfers into the ground under strong wind load. If it is not deep enough, the concrete foundation will simply turn out of the ground like a spade, on the handle end of which one leans. Mighty is the locksmith's strength when he works with the lever...

Sure. But it's not only the depth that has an influence. Also the base area of the foundation and especially the soil. Natural soil, compacted gravel, loose drainage gravel, "everything that was still left from the excavation"... Where it rests directly on rock, usually the connection between the concrete and the rock should be sufficient. If you like, you can drill a few holes and put reinforcement bars in, then nothing will come loose for sure.

Why don't you screw the posts directly from the back onto the L-stones?

Why don’t you screw the posts directly from the back onto the L-bricks?

It was discouraged due to the wind loads. Just to reiterate the initial situation: In the course of the house construction, the area where there are no L-bricks has already been excavated down to the rock or slate. The holes for the posts have to be made with a jackhammer. Still means 80 cm deep?

No, that was not discouraged. What was discouraged was screwing the fence on top of the L-bricks because there is simply very little "material" available there. Screwing from the back could also work, but you must not drill too deep under any circumstances ;) And better one more screw than too few.