How many troops would be required for deterrence, for the thousands of miles of borders that we have?
That's not an opposite notion, really. The opposite would be Mexican soldiers shooting down americans making a break for mexico. :-)
In any case, I am sure there would be a deterrent effect, but even with the military presence a lot of folks will try to take advantage of the holes. Enough of those folks being shot dead will be more than enough to turn the stomachs of all right-minded Americans.
There has to be a better way. We need to think of one, since illegal immigration is a huge problem.
And some will test the issue.
If the rules of engagement are tight, there is a high chance of the illegals evading the patrols...thus destroying their deterrent value.
If the rules of engagement are loose, they get shot, and CNN splashes a picture of 9-year-old Paco trying to stick his guts back into his abdominal cavity over America's breakfast. The troops are pulled out by lunch.
It's called "consequence management," and the concept completely escapes those who advocate sticking troops on the border.