I had a problem in which I couldn't drive a ground rod to ground my ham gear. The ledge is surfaced in some places and only a few inches deep in others. I finally decided to use the ocean. The ground wire would be long, but by stripping it and burying it in the lawn that would keep it from resonating on HF. There's only about 16" of it exposed before it goes in to the lawn.
I had some 2 gauge aluminum entrance wire lying around so I stripped about 60' of it. I then used a shovel and trenched the lawn and using a rod pushed the wire in to the trench and then stomped it back closed. By next summer it will have disappeared. This piece of ground is usually wet so that'll help with grounding on the lawn.
It's only about 25' from the building to the water's edge. After reaching the rock wall, I ran the wire down over the face of it and then buried it in the beach.
There's probably 25' of it buried in the mud. That's always wet with salt water.
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