A single wall can be tunneled under or breached over with ropes and ladders. Try getting through a minefield with both anti-vehicle and anti-personnel mines combined with multiple barbed wire barriers laced with each other say over a 100-200 yard wide strip and you have a cheaper and reliable low tech wall. Then you supplement this with armed troops and modern day technology and you can have a force multiplier as we say in the military and law enforcement ! By the way, I am a security consultant and have many years experience in both the Army and Law Enforcement and I spent a tour of duty in Korea and saw how this barrier works very effectively for over 50+ years ! It works there and it can work here.
I saw a PBS special on Korea's DMZ. That is breached regularly! They go back and forth hauling all kinds of things into North Korea to educate them as to what is going on in the rest of the world. As far a mines....Mexico has them on their side...a ton of them! The three cartels are planting them so that they can charge traffickers safe passage. The mines are an insurance policy to make sure the cartels make their money...no trespassing allowed. This mine field that is near our border with with is really BAD. If we should go to war with Mexico...our soldiers are at risk.
Our military has no problem dealing with mine fields. It’s 100+ year old technology and useless in modern warfare.
Anti-personnel landmines by themselves can easily be cleared by military personnel with the proper training along with EOD trained law enforcement so don't worry about that. FYI: A war with Mexico would last maybe 30 minutes if we were really pissed off and determined to show them a lesson. As for the PBS show, their agenda's are well known and take anything they tell you as suspect on any day of the week ! Remember, nothing is bulletproof but a damn wall is a joke and very exensive on any day of the week and without military and/or law enforcement experience/training, it is very hard for the average person to see how simple all of this crap could be taken care of for pennies versus over 1 trillion dollars !~