A licensed surveyor can determine and mark a property line. The surveyor researches recorded deeds and property descriptions and uses a variety of instruments to determine where to set markers exactly on the boundary between properties. The cost to the property owner depends on the nature of the terrain and the distance the surveyor needs to demarcate. It could vary from a few hundred dollars to several thousand dollars.
A close look at the area where the boundary between properties is believed to be located often reveals some clues to the exact boundary. Corners of properties are often marked by rocks or concrete markers. Old fenceposts may be located, even if wire fencing rusted away. Subtle changes in vegetation is a clue, too. If one tract was allowed to go wild before the other tract, then slight vegetational changes can result and help determine the boundary.
A property's deed includes the property's legal description. With that information, a high-quality global positioning satellite receiver is used to determine the property's corners and boundary. The result may not be as precise as what a surveyor could delineate, but it can be used in conjunction with other clues to determine the boundary close enough to satisfy property owners.
Depending on the size and location of the properties involved, sometimes a meeting with a neighbor can solve the dilemma. In many cases, being a few inches or even a couple of feet off the exact property line is insignificant to property owners involved. If the adjacent landowner agrees to a property line marked as accurately as possible, then the land-clearing project can proceed. This method is established in law and is the reason many deeds read a "certain" number of acres, more or less.