true but explosives would attract aton of attention, same with going over a large wall, and going under can be done but at least they cant find a hole in the fence and squeeze through, if anything detour them from crossing plus step up patrols on the border to stop even more of the crossing, i agree that crossing is going to be impossible to entirely stop, but at least get it to the lowest amount of successful crossings.
The explosives part was just an extreme example. I wouldn't expect anyone to actually try it. Going over would not attract much attention at all especially if you do it for example at night. Set up a ladder, climb over, boom done. Going around would be even safer, and for someone who's actually determined to get past the border it certainly won't stop them. It would definitely stop you from casually strolling across the border, but that's about it.
Then there's also the issue of cost. Depending on how fancy and big and thick you want your straight concrete wall to be; it could range anywhere from the high tens of billions to the high hundreds of billions factoring in labor and time needed to construct it. Spending that much money on something that's ultimately going to be ineffective? Total waste.
The Egyptian military killed 12 people and nobody cares. Everyone on reddit just blamed the guides for driving into a "banned area". The world is ready for death zones.
Eh. I could see it going differently with the context (especially with Mexico likely to get butthurt if it ever was implemented by a particular businessman) but you could be right. As long as the zones are marked off it could work, at least for people. There could be quite a bit of environmental impact if the thing isn't programmed to avoid wildlife or if they have to clear out tons of trees to build it. But if neither of those are a problem; a definite possibility.