Auxillary ground rods DO ABSOLUTELY NOTHING!!! For a warm up, here is a link to a newsletter from Mike Holt.
Rockyd says -Inside, or outside, grounding light poles, motors, building steel,etc, to an auxillary ground rod, and depending on an earth return path for current, will not facilitate in tripping an OCPD!(250.54~08 NEC)
From an old article, but principle is still the same
Mike Holt’s Final Comment
Answer No. 6 states "Don’t violate the Code. A building is to have one and only one grounding system. He can drive an extra rod if he so desires but he must tie it into the whole building grounding system."
I though and taught for many years that the NEC contained this requirement, but it doesn’t (never did as far as I know). As a matter of fact the NEC [250-54] recognizes the use of a supplement grounding electrodes, which is often required by CNC machine instructions, RF grounding grids, etc. The key is that the earth itself cannot be used for equipment grounding, but a supplement electrode can be installed without bonding it to the building grounding electrode system.
1999 NEC Section 250-54. Supplementary Grounding Electrodes
Supplementary grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in Section 250-118, but the earth shall not be used as the sole equipment grounding conductor.
If after reading this, you would like to make any updates, comments, corrects, etc. please let me know. I want to keep this question and answer updated to the current standard.