Why have them out there dodging bullets when a barricade/wall (where possible) would keep bad guys from coming across in the first place?
Well, go back and read the comments on building the wall.
In some places, it will be an engineering nightmare with topography and rivers to contend with.
A virtual wall strengthened with technological monitoring and weaponry can police those areas effectively.
I understand what you are apprehensive about. Why place individuals in harm's way needlessly? The answer we do not have to.