RF Ground

I have recently upgraded to a 2kVA P.T. driven coil.  For my first
"beginner" NST system, I drove a 8' rod through a hole in the basement
floor, and then ran about 40' of 1.75" tinned braid to the coil
upstairs.  Recent list archive searches have led me to believe that I
should replace the braid with solid copper, and I intend to install a
run of 3" strap.  My concern is that I need the last 10' of my
R.F.ground to be made from a more flexible material, for a number of
reasons.  How large a gauge of stranded wire does the list think I
require?  I am also considering soaking the ground rod hole with hot
salty water before runs.  There are long term corrosion issues, but it's
not a problem to replace the rod in a couple of years if this soaking
will improve performance.