We just heard from a friend of my Wife, who returned from a two week trip to Isreal, with her husband. She talked of an electronic border that Israel uses with it's neighbor, that is monitored around the clock from satellites. Maybe this might be the way to go with Mexico, she thought. After googling it, she found that Benjamin Netanyahu, is in the US talking with Trump about how they work. What America can learn from Israel's West Bank security barrier.
When I lived in Wales in the UK. We had a border. It was called the Severn Bridge. It kept the English out There is great rivalry between the Welsh and English. All good fun