You should never try to lay out a fence by eye. Use a 50- or 100- ft. steel tape to make measurements; strong white twine to mark the position of the fence; smooth, narrow, pointed boards or pieces of broom handles or brass curtain rods for stakes. ( Stakes cut from tree limbs or rough-split from boards are hard to drive straight and can throw off your measurements.)
When laying out a division fence, don't assume that you know where the boundary line lies. Take a look at your plot plan; You may find the line is not at all where you thought it to be. You may find it isn't even straight.
When you go outdoors, make sure that the pipes or other markers directing your line are the right ones.
Many strange things happen to boundary line markers. They get pulled out, driven below ground, moved. New pipes which can be mistaken for the old are often added in out-of-the-way places. The only way you can be certain about the position of a boundary is to study your property map and use a tape to verify the markers you find. lf you can't filed any markers, hire a surveyor.
Putting heads together with your neighbor may seem to be a sensible way to locate a common boundary; but he may not know any more about it than you do. So if the two of you decide the line is a foot closer to your house than it actually is, you lose the use (though not the ownership ) of a bit of property when you build the new fence.
Or if you build the fence closer to your neighbor's house than you should, you may spend money planting property that isn't yours; and when your neighbor moves, the surveyor for the new property may claim it.
Lets look at the case where the fence turns a 90 degree corner. To assure that the corner actually is a right angle, first you will need to nail three boards together into a triangle with sides of 3, 4, and 5 ft. After establishing the location of one run of fence and marking it with a string, place the triangle at the corner point with the claim. side parallel to the string. Then draw a second string taut ovals the 4-f t. side. The angle formed by the strings is exactly 90 degrees.