A fence is a freestanding structure designed to restrict or prevent movement across a boundary. It is generally distinguished from a wall by the lightness of its construction: a wall is usually restricted to such barriers made from solid brick or concrete, blocking vision as well as passage (though the definitions overlap somewhat).
It seems the world is obsessed with building things that restrict people. We need to build 'openings' in life. Do you remember when Germany tore down the Berlin wall? What a monumental moment in life! We need more times in history like that!