Answer:
To the best of my knowledge, lightning rods are (were) not driven in the ground, they are (were) placed on the roofs and apexes of building structures, to supposedly either ward off lightning, or to capture it and redirect it to the ground. I believe they are (were) then connected to each other and to a cable running to a stake in the ground, the depth of which made no difference, since the concept of the lightning rod was a sales hoax of the early twentieth century that relieved many a farmer of a few dollars.
Since I lived in the waning days of the lightning rod and had seen many of them installed, and had even sat through a sales pitch, I will continue.
A number of "scientific" premises were put forth as to how the lightning rod functioned - since buildings equipped with them were almost never struck by lightning (neither were the buildings without them), including:
- The lightning now strikes the rod (the highest part of the building) and is carried away to the ground. As soon as that was disproved by the fact that a healthy bolt of lightning would fry not only the rod, but the building too, a new "theory" was devised:
-Ok, well...errr, ahem...ok the lightening rod sets up an atmosphere around itself, of negative (or positive) ions (somehow) which repel the lightning and make it hit your neighbor's barn who did not buy lightning rods. Yeh, that's it!