If you think getting your neighbor to agree on your shared fence line is a challenge, you should consider what it took for Vermont and New Hampshire to agree upon their shared border: The US Supreme Court.  While the US Supreme Court in Vermont v. New Hampshire, 290 U.S. 579 (1934) settled the interstate dispute and established the shared border definition as the low water mark of the western shore of the western side of the Connecticut River, under state law the senior law enforcement officers of each state must inspect the border every seven years.

Article courtesy of Seven Days (https://vtdigger.org/2023/10/08/new-hampshire-vermont-officials-meet-in-upper-valley-to-agree-on-border/).