My understanding is that electrical equipment that is not "live" at
the time of the EMF attack would not be affected. It would be wise to
have any necessary batteries disconnected. Burying the items would
serve no purpose, other than security.
The way to protect gear that is not running is to place it inside a
sealed metal box (aluminum, copper, ect. The more conductive the
better) Note that the lid needs to be REALLY electrically sealed!
Usually RF "fingers" or Steel wool "O" rings are used to make contact
all around the lid. A simple wire to the lid just won't do it. For
small items, [Pack of CDs, DVDs, etc.] new empty paint cans are
perfect! Hey for fun put an old useless CD in your microwave! Great
way to get rid of your old "secret" files. Microwave might not be too
happy with the load, though.
However, any power cord (plus all wires in house and out to power
transformer) makes an antenna for the EMP as does any actual antenna.
IF the gear is to be operational at the time you must set it up as you
would to protect from lightning. Arrestors, grounds etc. Unplugging
power cords and antennas helps save gear because it disconnects the
"antennas" that pick up the damaging EMI.