[Trod Upon]

Probably airborne ground penetrating radar. It's now cheap and small enough to be put on tiny drones to ID landmines. More powerful, aircraft-mounted units have been around for quite a while now, to say nothing of satellite GPR. If you have a bunker, I guarantee someone knows about it. With kooks like Napolitano on the loose, every house with a basement foundation is probably in a database somewhere by now. There are obvious implications for those who would consider burrying weapons or items of value in advance of tyranny.

[Jonty30]

On another thread, somebody said they saw a video of this and that he had dug past the property line, that’s where I got that information from.

Unless it’s really important to question, I tend to take things at face value.