We don't need to shoot them to keep them out. Simply lobbing sleeping gas at them would suffice. Put them in a deportation camp accordingly to their home country. Ship them to the capitol of their home country.
End of story.
However ending the War on Drugs and the Welfare State would also halt their illegal entry, but neither of those will be done in this politically polarized climate, because you would need a Libertarian elected Government to do either.
...the right to due process, the rule of law, and the Constitution be damned.
Ya know what? Just stop it.
For you to trot out the US Constitution when it is politically convenient does not wash here.
Or for that matter, anywhere else.
This is the same premise as in drug crimes. If the marketplace for illegal drugs ( users) is reduced, the suppliers will find other places to sell their poison.
If in this country we stopped coddling drug users, as in if they are caught, put them to good use doing community service, they won't have time to put that shit into their bodies.
The sellers will go away.
Well, if this country would simply refuse any and all benefits to those who cross into the US illegally, the tide of illegals would stop, No jobs, no welfare, no goodies, no illegals.
Start by passing laws that include prison time for those who hire undocumented people.
As a trade off, if illegals do decide to take the risk and stay. offer them some kind of work documentation with official ID so they can be tracked and monitored. Make sure they pay their taxes. Let them become part of the system of which they wish to take advantage.