The buried wire is just that -- a single strand of insulated wire. It makes a big loop from the transmitter around your property and back to the transmitter. Prior to installing the wire, you may want to layout your boundary with either spray paint or a garden hose. This will give you a more visual representation of where your system will be. Skipping this pre-planning step may require extra digging on your part later should you decide to move the boundary.
You need to bury the wire 1 to 3 inches below the surface of your yard. Although the system still works if the wire is not buried, the probability of the lawn mower cutting the wire or someone tripping over it is 100% if you do not bury it.
Spool of 18-gauge, multi-stranded wire
Most basic underground or wireless pet fence kits come with a 500 foot roll of 18 gauge multi-stranded wire, wire nuts and a wire fastener. The 500 foot roll of wire is sufficient for about 1/2 acre of land. If you prefer to fence in a larger area for your pet, you can purchase additional packages of wire and training flags at a minimal cost.
You should also know that when laying the wire around your yard, you can also enclose swimming pools, vegetable/flower gardens, or any other area that you don't want your pet to access. This is done by twisting the wires together between the secondary enclosure (the pool or garden) and the primary enclosure (your yard), as seen in the image above. Twisting two wires together cancels the signal, allowing your pet to roam freely between the boundaries of each enclosure.