When building a wooden fence, set fence posts about 15 cms to 20 cms apart depending on the type of fence, terrain and purpose of the fence. Set the corner post first and align all the posts in between. Space and dig the post holes. Set posts about 8 mm into the ground and add gravel at the bottom to provide drainage. Treat the wood and secure with concrete allowing it to dry then build a mound around it for easier drainage. Provide extra support at the corners. Finally, attach rails to the fence posts starting with the top and bottom rails.