Just for my personal information, wondering if someone played with buried
or submersed antennas and (especially from 40 meters going lower in
frequency) get some interesting result.

I once read an article in which it was stated that in a simple vertical, the
element current it restricted by the ground current, and any attempt to
increase the ground curent resulted in an increase in efficiency. The
article went on to state that an antenna having maximum contact with the
ground would be the most efficient, and in test a 1/2-wave dipole burried
underground could have an efficiency approaching 98% that of a dummy load.
The advantages are numerouse, such as the lack of an antenna support
structure, but for VHF arrays there could be a huge problem with direction
since the torque required to turn only a 2m 8-ele Yagi would be over a ton.