There are some rules you should know about on heights, spacing and amount of post in ground. For a treated pine post, star picket and wire or mesh fence, half the post height should be below ground level. So a 1200mm high post should be in the ground 600mm and so on. For a box end assembly or 'H' brace, the horizontal brace length should be 2.5 times the post or fence height. So a 1.2m high fence would need a 3m horizontal brace.
1.2m high farm fence diagram
