A TDR should work just fine for this purpose. You're just launching a wave into the rod, and then measuring the reflections.
In therory yes - it would, but I have not seen a product yet that would. You could measure the VOP (Velocity of Propogation) of a rod of known length, and that known length is compared to find the length of rod you have. I have used mine for finding shorts and opens to +/- 2' over 100' and it has been pretty accurate. But most of th e TDR units out there need two parrelel conductors to operate - otherwise they get very wierd readings, as most were made for cable fault finding, and also measure impedance changes. (Thats why I mentioned that with a refferance rod - it might be possible) Not to mention varying soil conditions etc....
