Richard wrote:
Has anyone ever bored a hole into the ground and dangled a radial or
counterpoise down it instead of burying a radial 6" horizontally under
the ground or stringing out a counterpoise?

Any promise in doing this? Or is it a non-starter?

Radials basically serve the purpose of improving the apparent
conductivity of the soil at the base of the antenna (e.g. less loss than
a simple stake in the ground).

A goodly portion of the loss of an antenna like a vertical is in the IR
losses of the RF current flowing in the surface of the soil (where
"surface" depends on the RF properties of the soil, skin effect and all
that).

So, burying deeper probably doesn't help this (e.g. you want to improve
the conductivity at the surface).