Dig holes where you will erect your posts. Make sure to dig deep enough so that the posts can go down 18 inches.
Erect the 5 x 6 inches posts, setting them at 6 1/2 feet intervals.
Erect the intermediate posts (3 1/2 inch square) for added strength.
Pour concrete into the holes where the base of the posts are erected. This will strengthen and stabilize the posts.
Screw or nail the planks into position. Place them in three rows in each section. Use galvanized screws or nails to ensure that they are rust proof.
Use a spirit-level to make sure that the planks are horizontal.
Connect or butt-join the planks at the center of a post. Try to stagger each plank on each row to make sure they are more stable.
Fit a post cap on each post to give a finished over-all appearance. This can also help protect the posts.