Build a Shadowbox Privacy Fence
To set the posts, start by filling the bottom 4 to 6 inches of the holes with gravel, which will allow some degree of drainage to help prevent rot at the base of the post.
It’s important to set all the corner posts first. If you have a helper, they can hold the post upright while you use a hand level to make sure it is plumb. A post level is also helpful, because it straps around the post while placing level vials on two sides of the posts. A post level frees your hands, which is very helpful if you’re setting the posts alone.
Once you’ve established that the post is plumb left to right and back to front, you’re ready to add concrete. However, you must brace the post in place while you add the concrete. If you have a helper, they can hold it for you. Otherwise, you’ll need to nail some scrap lengths of wood (I use 1-by-2’s) that extend from the post to the ground to act as moveable braces, with the nails serving as their pivot point for adjustment. Plumb the post, adjust the braces to hold it plumb, and then add the concrete. Use a sledge hammer to pound the posts into the ground once surrounded by concrete, then recheck for plumb and adjust if necessary. It’s a good idea to leave the braces in place while the concrete sets.