Copper & Salt

I have asked this question before and did not get an answer.  I am thinking
about putting in a new ground system this spring (if it ever warms up, about
-25 degrees in Spokane).  I am planning to use four 8.0' copper rods driven
in with a ground rod in each corner of an 8.0' square pattern.  Then solder
them together with copper pipe.  My question was, is it a good idea to bury
them with salt pellets sprinkled around them or not.  I know oxidized copper
is not a good conductor.  Because of the frequency and current is this oxide
not a problem?  How long can I expect this system to last before it is
corroded to the point where it is not effiecient?

My previous two ground systems were close to flowers and the lawn so I could
not use any salt.  This new one will be buried under my gravel driveway.

Ed Sonderman