If we were to put these on our southern border, I would put them between 2 walls. The first being right on the border itself, and the second being a few feet in. The only people who would be killed would be those who violated the first wall. Innocents on the outside of either wall would not be in danger.
Maybe as a later stage, but you can build, buy, set up and feed these sentry guns for a lot less money and almost no time as compared to a wall.
Maybe build the walls later, but for now, throw up a couple of cyclone fences with signs and start installing sentry guns.