Robert Frost famously disparaged the idea that "good fences make good neighbors." Unfortunately, that kind of idealism can result in one person taking advantage of neighbors. In some cases, a solid fence or boundary line is important to maintain neighborly relationships. If one neighbor decides to plant or build on or over a property line, it can cause serious issues. If the person whose property was violated doesn't take steps, the law may eventually allow for the person violating the property lines to have the boundaries adjusted. If your neighbor has overstepped that line, you need to take action.