That line comes from an old poem. Boundary issues are the divorces of real estate law, tempers can flare, people can really dig in their heels over small chunks of property that are really not important to anyone. These issues can involve where a boundary line between two properties is located, or, whether a building is on one property or another. If you have a boundary line dispute the first thing to think about is whether the area in dispute is really important to you. It is not worth fighting over a few feet of land that does not have a building, driveway, or other important amenity on it, you will usually spend more on a lawyer than whatever the piece of property is worth. If the issue is about a substantial chunk of property, or, concerns access to a road, lake, or driveway the stakes can be higher.
If you have a high stakes dispute the first step will be to get a good survey. If the neighbor has been using your land it is not always easy to end the use, in many cases they can claim what is called Adverse Possession if they have been using for more than 15 years. If the neighbor has been using some of your land for a long time you will want to take a close look at whether Adverse Possession applies. For someone to possess property by Adverse Possession they have to show use that is hostile, open, exclusive, and continuous for at least 15 years. The 15 years can combine with whoever owned the property before them, meaning if the owned the property for 5 years, and the person they purchased from owned for 10 years they can combine those time periods for a total of 15 years. Openly means that the use has to have been clear, i.e., a building, or a landscaped yard. Hostile and exclusive means that it is not open to the general public, i.e., it is clearly their yard, or restricted in some way.
If you are involved on either side of an Adverse Possession issue the facts of your particular case will be important, every situation is different, your facts will determine if Adverse Possession applies to your situation. You will want to get good legal help to navigate through the legal system.