The best way to lay out a fence is with batterboards. They are a bit fancier than stakes and string but allow you to reposition the string without moving the stake. For string, use mason's line — it won't sag like regular string does. If the fence has two or more sides, they need to be at right angles to each other. It's not the sort of thing you can easily check with a square, so you'll have to measure the diagonal between two points near the corner. Once you've run the lines, you can put tape on them to mark where the posts will go. Depending on the fencing you're using, the posts will be either 6 or 8 feet apart.
There are 4 steps to completing this project:
Build a pair of batterboards for each run of fencing. Start by cutting points into the ends of two 2-foot 2x4s. Nail a 2x4 crosspiece to them about 2 inches from the top. Drive the batterboards into the ground about 18 inches beyond the planned end points of the fence. Tie mason's line to one of the crosspieces, stretch the line to the other crosspiece, and tie the line in place so it's taut.
Hang a line level on the middle of the line. Drive one of the batterboards farther into the ground to level the line, if necessary. Measure from a fixed object, such as the house or patio, and slide the line along the crosspiece until the line matches the exact path of the fence. Drive more batterboards and stretch line to lay out adjoining sides of the fence. Level the line as needed by driving one of the batterboards farther into the ground, then adjust so the line replicates the path of the fence.
Start at the corner where the lines cross; measure 3 feet along one line and mark the spot with tape. Put a piece of tape 4 feet from the intersection on the other piece of line. The lines are square if the distance between the pieces of tape is 5 feet. If they're not square, slide one of the lines along the batterboard until they are.
Drop a plumb bob from the corners that the mason's line forms. Mark the spot below the plumb bob with chalk. If the fence ends without forming a corner, measure along the line to lay out the end point. Mark it with tape, drop a plumb bob, then mark the ground with chalk. Measure along the mason's line, and put tape on the line to indicate the position of the fence posts. Drop a plumb bob from the tape and mark each spot with chalk or a piece of paper and a nail.
