The relationship of a "grounding" system along with a "surge protection" system is essential in providing the protection from a surge or lightning. A protection system cannot function if only grounding or surge protection is deployed, exclusively. In these cases the function of a grounding system is to be the depository of a surge which is diverted to it, by the surge protection devices. The function of the surge protection is to divert and equalize the potentials on all connected lines to the grounding system.
The two systems function as a single system in the event of surges or lightning.
The ground rods begin to deteriorate the day they are inserted into the ground. Depending on the soil and moisture content the rods will corrode quite rapidly. In addition, it is relatively common for a ground rod to become encased in glass as a result of high current / surge energy and the sandy composition of the soil. A 5 ohms earth can become a 50 ohm earth in only a few years. It is essential that the ground rods are accessible so that they can be measured as part of an annual preventative maintenance program. It is typical to drive the ground rods though a :pull-box" with 6" - 10" of the ground rod exposed so that measurements can be taken with a clamp-on earth tester. Do not bury the ground rods below grade when they cannot be accessed
There are numerous schools of thought as to what constitutes a good earth. Telecommunications companies have , in the past, specified a 5 ohm earth for telephone exchanges (CO's), while some other industries have opted for a 25 ohm earth. There are a number of key factors in play that have to be considered when determining an acceptable earth impedance at a site
Finally, simple economics and the soil impedance play a role in determining the desired impedance of an earthing system. Any attempt to achieve a 5 Ohm earth at a site in the desert or at a rocky pasture, may significantly drain your resources.