The most likely place for a fence post to become damaged is at, or just below, ground level. At this point, the wood is almost permanently damp, causing it to rot. Once a post is rotten, it can give no support and the section of fence butting up to it tends to lean out of alignment.

To repair the post you must cut off the affected part and attach a supporting spur. This involves temporarily supporting the fence and then digging a hole around the post about 60 cm square and 30 cm deep. Saw off the rotten part of the post once it is completely exposed and bolt on the concrete spur - 15 cm or 20 cm coach bolts are suitable. The straight face of the spur should be against the post. When it is in position, use a spirit level to check it is upright. Hardcore should then be packed around the bottom of the spur and the hole filled with a coarse concrete mix, finished at ground level with a slope to drain rainwater off.

Another method for a fence post which is not exposed to strong winds is the use of a metal spike. After the rotten part of the post has been cut off, the ground must be tightly packed back into place. The metal spike is then driven hard into the ground, while gently holding the fence out of the way. The post is then hammered into the spike's square cup and bolted in place.