It ABSOLUTELY depends on what type of soil, and the size of the electric fence run. Around a tiny little coop in a backyard, anything will be overkill. Even in poor soil.It probably depends on the kind of soil, and how wet it usually is.
The fence company might be showing what works for the most difficult situations.
Using my 30 mi charger (2.x joules) and 3 hot wires around less than a half mile of fencing (each of three legs) on my dry sandy clay soils, even three 8' deep ground rods wasn't sufficient. I had to drive another ground (albeit shorter) at each corner, and in the middle of the long sides, all connected back to the charger's ground system. When we go three weeks w/o rain, the soil is such a poor conductor you can tap the wire with the back of your thumbnail and get an annoying jolt. OTOH, when it rains as it did last night, and the soil is conducting well??? I can hear the discharges off the fence from 30 feet away, further in places.
The fence company made some "assumptions" for that diagram. As usual, its the minimum for the typical on good soil. The OP, however, benefits in that the area they are enclosing is (relatively speaking) miniscule compared to the typical electric fence system - whose lowest point of effectiveness is determined by the distance and soil conditions between the furthest fence location and the ground rod(s). Here, instead of being measured in 100s of feet, or thousands, its likely less than 20 feet.
OP is actually building a lightning rod, effectively, by creating a concentrated area of negatively charged ground. Not as bad as it sounds though, because *most* lightning is negative charges in the clouds to positive charge on the ground - the e-fence creates the reverse of that condition. That's why the negative goes to ground.
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