They say, yeah, well, they can still tunnel under the wall.
True. BUT, HOWEVER, there are modern technologies that can detect tunneling … new kinds of seismic detection … developed in the pursuit of fracking in the United States to develop oil and natural gas … [very politically incorrect] …
… AND … ground penetrating radar … which has been around a long time, but which has been developed during the “campaign” against IEDs. Improvised Explosive Devices.
But both of these can be used to detect tunneling.
And I suspect other technologies, as well.
It’s why it is important to “do science”.
By the way, if you detect a tunnel, all you need to do then is to call up a ready-mix concrete truck, and fill up the tunnel. You use what they call “a soupy mix” … very liquidy … so it flows smoothly into all the voids and through all and any twists and turns. Not trying to build a foundation for a bridge or anything like that.
But the concrete will harden up. And that’s the end of that.
It’s cheap and fast. All you need is a cell phone and a credit card.