Abstract: An outrigger arm assembly to prevent a would-be intruder from successfully climbing over a fence. The outrigger arm assembly is mounted on top of the fence. Each hollow fence post is interconnected to a hollow outrigger arm by a replaceable collar which breaks when a load in the range of 20 to 30 pounds is applied to the outrigger arm, resulting in the downward movement of the outrigger arm, and the fall of the climber. The assembly also includes a movement sensor, within the hollow arm, which is activated and provides an alarm signal, when the outrigger arm is moved more than a predetermined number of degrees, such as the downward movement of the outrigger arm. The assembly further includes a coiled spring, positioned within the hollow fence post and extending into the hollow outrigger arm, by which the arm is automatically returned to its original defensive position, after the load is removed.