Place the two 4-by-4 pieces on a flat surface. Lay one of the 2-by-4 pieces on top of the two 4-by-4 pieces and situate it so that the ends of the 2-by-4 are even with the edges of the 4-by-4 pieces, and the edge of the 2-by-4 is 3 inches from the ends of the 4-by-4. Screw the 2-by-4 to the 4-by-4 pieces by driving screws through the 2-by-4 and into the 4-by-4. Use two screws for each 4-by-4.
Measure 6 inches from the bottom edge of the 2-by-4 you just placed and place the second 2-by-4 on the 4-by-4 in the same manner as the first piece of 2-by-4. Screw this piece to the 4-by-4 by driving screws through the pieces of 2-by-4 and into the pieces of 4-by-4 using two 2-inch screws.
Dig two 6-inch-deep holes with a post hole digger in the location of the fence. These holes should be 4 feet apart. Place the frame that you just constructed into the holes and pack the holes with the dirt you just took out. Make sure that the frame stands up straight.
Place one of the 8-inch planks against the 2-by-4 pieces of the frame. The bottom of the plank should be on the ground and the top should go 6 inches over the frame. Screw this piece to the 2-by-4 by driving two 1-inch wood screws through the plank and into the 2-by-4.
Place a second plank next to the first so that it is even with it and screw it to the 2-by-4. Repeat this process for the rest of the planks until the frame is covered.