Down in Alabama we sink fence posts a minimum of 2 feet, but the deeper the post is, the stur- dier it will be. Loose or unstable soils need more depth in order to support the fence. A good rule of thumb is the "One-Third Rule", which says to bury at least one- third of the post height for a wooden fence, so the minimum depth for a 6-ft. tall post is 2 feet. Taller fences need deeper posts. However, different areas may require even deeper post depths. For building in cold climates, you should consider the frost line. Frost below a fence post will push up on it, causing it to move, tilt or possibly fall over. The colder the climate, the deeper the frost line will be. You should dig holes for fence posts at least 6 inches deeper than the frost line. For this reason, many building depart- ments have codes for minimum post depth. They may also require permits and specify construction methods. Check with your building
department for guidelines. Some neighborhoods may also have cer- tain architectural guidelines or “covenants” that restrict design. When spacing the posts, be sure not to spread them wider than the length of your fence rails (usually 6 to 8 ft. on center). The shorter the distance between posts, the stronger your fence will be. When measuring, keep in mind that the ends of the rails can be toe-nailed between the two opposing inside faces of the posts, or they can be face-nailed to the outside of the posts, with the rail-ends butting together in the middle (like we did with the fence shown in this article). Once, you've determined the course of your fence and you know the planned location for your posts, make sure there are no underground obstructions. Before digging, you can dial 811 nationally to get underground utili- ty lines, cables and pipes marked for free. Also, double-check that the location of your fence won't cross onto a neighbor’s property.
POSTS Pinpoint the location of each corner post first. Drive stakes into the corner-post locations and con- nect them along the fence route with string. Walk the perimeter
The first phase of building a fence is to lay out the fence with stakes and string and set the corner posts. A good rule of thumb is to dig a hole 1/3 the depth of the overall post height. A 6' tall post requires a 2' hole and an 8' 4× 4.
Post levels are handy because they feature level vials on two adjacent faces of the post, plus they strap onto the post and free your hands.