[VRWC_minion]

Usually need two sensors in a beam interruption device and how does one bury this type of device without interrupting the beam oneself.

Here is a solution but its scary. What if the receiving beam is placed on the train itself. What if the train is fitted with a device that receives the beam and sets off an explosion on the train.

[Rebelbase]

"What if the receiving beam is placed on the train itself. What if the train is fitted with a device that receives the beam and sets off an explosion on the train."

That reads like blowing up the train to find the bomb.