Install Bottom Fence Rail
For the bottom row, you need to find the highest ground area, then measure up a desired distance. You want to place the rails as low as you can to the ground. This give less room for your dog to wiggle under and escape. Do let the rail touch the ground because the ground will rot the wooden fence rails. Use your chalk line to mark the approximate locations for the lower fence rail.
Before attempted to place a screw through the fence rails, pre-drill a hole. 2 x4′s can split without pre-drilling and it allows you to insert a screw with just enough coming through the rail that you can use the point of the screw to hang the rail while you position the drill with the driver on the screw.
Measure the distance from the centers of the fence posts and cut a fence rail. Place one end of the fence rail in the center of the post and use one screw to hold the rail. Use your long level to put the rail on level and screw the other end of the fence rail to the fence post. Continue this process around the fence perimeter.
Install The Top Fence Rail
From the center of the bottom rail, measure the width of your welded wire fence fabric up. This will be your center for the top rail. You want to staple the top and bottom of the fence material near the center, so centering the widths will allow for this. Check with your long level that the top rail is square and level and install the top rail.
Install Vertical 2×4′s For Padding
The vinyl coated wire mesh fence fabric need a surface to staple to. For this purpose, a 2×4 is placed vertically on the fence post and connects to the top rail. Measure the distance between your top and bottom rail and cut a 2×4 that will fit between them. Nail or screw the 2×4 into place.
You Now Have A Rectangular Box
Your end result is a rectangular box to staple the vinyl coated wire mesh fence fabric to. Repeat making these boxes until you have a length that you can staple an entire roll of material to. I would stop every time this length is reached to ensure that your measurements and installation is as expected.