Fence posts serve as a fence's backbone, so installing them properly in the ground plays a key role in determining the overall success of your fence. Fence posts fall into two major categories: wooden posts and temporary posts. Wooden posts make up permanent fences and require you to dig a hole for solid post placement. You must pound temporary posts directly into the soil and they include an assortment of thin, easy-to-install materials, such as steel T-posts, metal rebar posts, fibreglass posts and tread-in plastic posts. As a rule, expect fence post installation to take up to half of the overall fence installation time, especially if you're installing wooden posts.
Wooden fence posts
Install wooden corner posts for your fence. Using a clamshell posthole digger, excavate a hole deep enough to contain the bottom one-third of the post's length. In most cases, this hole will be 60 to 90 cm (2 to 3 feet) deep.
Insert the base of the first corner post into the first corner post hole. Stand the post upright and hold a hand-held level against the side of the post to verify that it's straight, shifting the post, if necessary, to level it in the post hole.
Pack loose dirt around the base of the post with a tamping rod, adding the soil in small increments until it forms a well packed, slightly rounded mound around the base of the post, which helps promote proper rainwater flow. Repeat this entire installation process with each remaining corner post and line post. Position line posts as close as 2.1 cm (7 feet) apart for board fences or as far apart as 27 m (90 feet) for a permanent electric fence.
Temporary fence posts
Sink steel T-posts into the ground to serve as corner fence posts for your temporary fence. Press the base of the first steel T-post into the ground marking the first corner post location.
Lower a manual post driver over the top of the T-post. Grasp the post driver handles, then raise and lower the driver, bringing its top down forcefully against the top of the post to drive the post into the ground. Sink the steel T-post to a depth of 30 to 40 cm (12 to 16 inches). Repeat this installation process with each remaining corner post.
Insert temporary fence posts along the perimeter of the fence to serve as line posts. Sink steel T-posts in the same way you installed the corner T-posts, driving them into the ground as close as 3.6 to 4.2 m (12 to 14 feet) apart for barbed wire and woven wire fences or as far apart as 12 m (40 feet) for temporary electric fences. Hammer metal rebar and fibreglass posts 15 to 25 cm (6 to 10 inches) into the ground in 3 to 4.5 m (10 to 15 foot) increments, depending upon the fencing material in your temporary fence. Position tread-in plastic posts 3 to 3.6 m (10 to 12 feet) apart, pushing the base of the post into the soil until the tread is flush with the ground.
The tops of fibreglass posts often shatter when subjected to the repeated blows of a hammer during the fence installation process. Prevent this from happening by placing a spent shotgun shell over the tops of these posts before hammering them into the ground. Most wooden fence posts are available chemically treated to prolong their lifespan to 20 or 25 years. If you'd rather use non-treated timber, stick with a naturally rot-resistance species, such as black walnut, osage orange or cedar.