Along with electrocution, commuters who ride on top of trains in Indonesia now have to worry about Goal Bola-Bola; wires strung with concrete balls hanging above the train tracks.

Implemented by the Kereta Api, Indonesia’s state railway, the Goal Bola-Bola are dangling grapefruit-sized chunks of concrete. Hanging off of poles above the railways, the concrete balls hang the entire way across the tracks and would easily knock off any one of the hundreds of free riders who surf the trains on their commute everyday.

The concrete balls are the latest innovation in a string of attempts to stop free-riding that has included greasing the tops of trains with oil and barbed wire.