If you are planning on building a fence, you have several options regarding how you set your fence posts. Traditionally, you would dig holes then use the loose dirt to hold the post in place. While this may work for a while, eventually the dirt can become soft from moisture and shift, moving your fence post in the process. If you want a stronger option to set your fence posts, consider fixing them in concrete.
Place wooden stakes in the dirt at either end of your fence path. Tie one end of your rope to one of the stakes, pull it as taut as possible, and tie the other end to the opposite stake, creating a straight line.
Insert wooden stakes in the ground along the line approximately 2.4 m (8 feet) apart. This will provide you with markers so that you can dig your holes in a straight line.
Dig holes with the post hole digger where there are stakes. Make sure to dig the holes at least 45 cm (18 inches) deep.
Pour some of the cement mix into a wheelbarrow and add water. Mix with a shovel. The concrete should end up with the consistency of thick mud.
Place a post in each of the two end holes. Use the level to make sure it is plumb, and fill the hole with the concrete. Allow the concrete to dry overnight.
Tie the string between the two posts on either end of the fence line, and pull it as taut as possible to provide a straight line.
Mix the rest of the concrete with the water in the same was as you did in Step 4. Place the posts in the remaining holes; stand them up so they are just touching the line; make sure they are plumb, and fill the holes with concrete. Allow the concrete to dry overnight.
When doing this project, you should use an instant concrete mixture. You can buy one at a DIY centre.
Make sure that the posts are all touching the line in roughly the same location and that none of them is "pushing" the string out of the way. This will create an uneven line for the fence.