Well no body quite hit the nail on the head with this one.
Ground rod have what is known as a sphere of influence. The sphere of influence is twice the depth of the ground rod time the depth of the ground rod as a radius.
Except it's not a sphere. Think more a half ellipse.
The practical implication is that spacing ground rods closer than twice their length (e.g. closer than 16 ft for 8 ft buried length) doesn't have as low resistance as farther apart.
A 8 foot ground rod sphere of influence would be 16 feet deep by 16 foot in diameter. A 10 foot rod would have almost twice the sphere of influence.
Not quite true, and the "volume" of the sphere isn't particularly important. In your example, the 10 foot rod would have 75% lower resistance than the 8 ft rod. (approximately, and only applies for SMALL differences in length.)
Now for some rules of thumb;
• Jet the ground rod in, burry the ground rod in, screw the ground rod in it doesn’t matter. The earth will settle around the ground rod to 95% compactness within a week.
• The deeper the ground rod the better.
• One deep ground is much better than a dozen shallow grounds.
Just not true. Unless you're talking 10 ft and 1 ft or something extreme (or if the dozen rods are all driven in a small area). The same reason that driving two rods too close together isn't a whole lot better than a single rod also applies to doubling the length of a single rod. That is, the top half of the rod is (if you think about it) one half rod length away from the bottom half.
A 10 ft rod is sort of like driving 2 5 ft rods 5 ft apart.
• Ground rod diameter doesn’t matter except as to the length of time it takes to corrode the ground rod.
• If your copper wire is buried to the ground rod and the ground rod is buried better to cad weld to the rod.
• All grounds should be bonded with a number 6 solid copper wire as per NEC code. This includes the station and the AC Panel.
• A big Hilti hammer drill is the easiest way to plant a ground rod.
• Cover a ground rod sticking out of the ground with white PVC. They hurt like hell when you rack your ankle on one.
I'll agree with all those..