Institute a “shoot to kill” policy AND build the fence, and it’ll be pretty damn close to being 100% effective.
We don’t need a “shoot to kill” policy, or landmines.
All we need is an actual wall. Put concertina wire on top, monitor it, and it will cut down the vast majority of border incursions.
There’s always going to be a way to get in. Right now, you can stroll across the border in the middle of the night with a gallon jug of water to get you through the next day, and you’re in. A wall starts making that harder. Women, children, the elderly - won’t be able to scale the wall so easily.
But we don’t have the money. Well unless we get rid of the drone surveillance, government cameras all over the streets, stop buying up all available ammunition, hiring 17,000 IRS agents to enforce commie-care... etc etc etc.