While it is legal to build a fence right up to the property line, it is illegal to cross even an inch onto a neighboring property. As a result, most fence builders install within a foot inside the respective property line to avoid causing disputes with neighbors.
Those who plan to build their own fences often study their property plats or order a new survey of their property to avoid crossing the property line. They also generally discuss their plans with neighbors. It is helpful to share plans for a new fence in case the neighbors are planning to build their own fence. Potential pitfalls of failing to discuss fence building plans include two fences built too close together, which often looks cramped, or too far apart, which results in a narrow strip of lawn that no one can reach to mow.