Set out the intermediate posts and try to keep them spaced evenly with no more than 3m between them.
You can use mortice arris brackets to mount the arris rails to the post which will stop any movement from the arris rail.
2 arris rails are required for 1.65m, 1.8 and 2.1m fence posts. 3 arris rails are required for 2.4m fence posts, and 4 feather edge boards are required for each 300mm of the fence.
Arris rails are a length of softwood treated timber cut diagonally to produce a triangle shape. These are to be secured to the posts to form a frame for feather edge to be attached to form the fence.