> In most (all in the US?) jurisdictions a law regarding prescriptive easements or adverse possession probably makes your neighbor's actions legal. After enoug

> In most (all in the US?) jurisdictions a law regarding prescriptive easements or adverse possession probably makes your neighbor's actions legal. After enough time, the neighbor acquired the title to the land through adverse possession and the fence became legal. Before that, the fence was illegal as it was built on property that the neighbor did not own.