Well, we did our electric fence a totally different way...... using the wire fencing itself as the 'ground'......and it works great!
If you use a ground 'rod'.....then the animal you are intending to shock must be standing on the ground 'and' touching the hot wire at the same time, in order to complete the circuit. This is great for horses/cows/goats, etc; but also why a bird can actually sit on the hotwire 'without' being shocked!
Our run has 2" x 2" woven wire fencing as it's 'walls', with hardware cloth running 3 feet up the 'wall', from the ground......and also 3 feet 'out' from the bottom, as an anti-dig 'apron'. Our ground wire is attached to the wire fencing itself, and the hotwires are held away from the fencing, approx. 2 inches, with plastic insulators.........so the whole system is grounded 'without' the use of ground rods! (You can touch the wire fencing itself, and NOT get shocked.) And we have a total of 4 strands of hotwire running (placed at approx. 8 inches, 16 inches, 42 inches, and at the very top of the run 'wall').....
This way, if a creative racoon scenses the 2 bottom wires are hot, and decides to 'jump' onto the fencing, to land 'between' the 16 inch hotwire and the 42 inch wire......he will still get shocked, even though his feet are actually not touching the earth! (Think....bird can sit 'on' hotwire with no shock.) This would not be the case if one only uses ground rods!
So you actually can have a more effective anti-predator set-up 'without' using ground rods!
p.s.
I always, always unplug my system when the chickens are free-ranging outside the run.
I know the electric fence folks say it would be safe if a chicken were to get zapped.............but I can't even think of that...........so it's disabled when they'll have access!
Believe me, I have touched the hot wire by mistake a number of times in my life, and it is NOT a pleasant experience!!! Esp. when you are bending over to pick something up, and the zap hits your BUTT!!!
