According to Michael Roback :
I ran some electrical in a wall that is closed up and wonder what I can get
in between the electrical and wall to prevent someone from drilling or
nailing though it at a later date. Can't get a dottie plate in as the other
side of the wall is closed, but I can fudge a piece of sheet metal or
someting in there. What should I use and what guage? And how do I affix
it, glue???

If it's just loosely fished thru the wall cavity, you don't need to do
anything. If you were to drive a screw, nail or drill into it at a later
date, it'd just push the wire out of the way and be very unlikely to be
a problem. Besides, once you got thru the wall surface, you'd stop drilling
anywho.

Steel nail guard plates etc. are for when the wire is held in position
less than 1 1/4" from the wall face (measured from stud wall surface).
Ie: cable held by staples or holes drilled thru the studs.

Indeed, most electrical inspectors will permit wire directly in contact
with the back of drywall _if_ there's nothing solid behind the wire (ie:
no reason to drive a surface fastener there).

Eg: on the bottom of ceiling joists parallel (and between) ceiling
lathe used to support drywall. They insist on an additional 3/4" in
depth when the wire crosses the lathe.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.