A lot of information here

http://www.postfinder.com/post/24221294.html

In part:

Placing The Ground Rods and Making the Connections Once you choose the type of metal to be used for the ground rods, and bought enough to adequately ground the size energizer you intend on using, the next step is placement. Here again there are a couple of things to consider. First of all an effort should be made to try and segregate the electricity that is flowing back and forth to the fence from the main service panel and other circuitry. There is a tremendous amount of electricity flowing and it is wise to try and keep the two Systems separated as much as possible. The actual placement of the ground rods is dependent on where a majority of the fence is in relation to the energizer. The ground rod system should be thought of as a big antenna. The closer the system is to the area where most of the electricity is expected to flow back from, and the more spread out the system is, the better. The general recommendation for the distance between multiple ground rods by most fence manufacturers and distributors has been to place the rods about ten feet apart.

The National Electrical Code recommends placing rods in multiple ground rod systems twice the length of the rods apart. For example, two eight-foot ground rods should be placed at least 16 feet apart. What is ideal for an electric fence may or may not fall within these recommendations but it is a good place to start. The important thing to remember is to keep the rods spaced far enough and even enough to act as a good electrical 'antenna'. Once the rods are in place the next step is to connect them all together. Starting from the energizer to the first ground rod, use properly insulated electric fence lead-out wire designed to handle the large amounts of electricity flowing through the system. This will help segregate the electricity coming back to the energizer from the grounding system of the main service panel and also keep the wire from coming in contact with other metal objects which could them become part of the system and actually carry small amounts of electricity. Aboveground structures can also provide another route for lightening to enter the system.

After the first ground rod it is up to the individual whether they want to make the connections between additional rods with insulated or uninsulated wire. Regardless of what wire is used, always use the same gauge, or larger, wire that is used in the rest of the fence system. The actual connection between the ground rods and the wires between them is extremely important. From purely a maintenance standpoint, ground rod connections should be made where they can be easily checked using approved ground rod clamps made of the same material as the metals it is connecting. Every spring a routine maintenance practice should include taking apart the ground rod connections and cleaning them to remove corrosion. Throughout the summer and winter the metals expand and contract continually allowing corrosion to occur that will reduce conductance. A little time and a wire brush can keep the system in good working order.