Concrete posts are normally dug into the ground and the post secured with either a dry mix ballast and cement (about 7 to 1 mix with no extra water added) rammed up around the post or postmix (follow directions on the bag). The amount of each that will be required will depend on the size and depth of the hole. Try to keep the hole diameter fairly tight around the post, 200 to 250mm (8″ to 10″) is good. Generally, for any fence height, the hole should be a minimum of 600mm (2′) deep. For fence heights over 1.5m we recommend that the hole depth is increased to a minimum of 750mm (2′ 6″). For morticed posts, the depth of the hole is preset by the manufacturer. We do not recommend reducing the hole depth by cutting off the bottoms of concrete posts.