Post guards and shoot crossers on sight. Illegal crossing stops very very quickly.
I remember how candidate Trump used to fire up rally crowds with repeated promises to put up seven miles of fencing improvements planned under the Obama administration. Those were exciting times!
A fence is eight feet high and a wall is 50 feet high!

Was expecting that at a minimum.
I always said put in a mine field instead of a wall and it would be more effective and cheaper. the only problem is that we don’t have the stomach or it.
“While the current wall differs from the massive barrier Trump repeatedly promised in campaign rallies during the election, the new wall is a considerable upgrade from the chain-link fence that once sat there. “ So, how useful is it?
I think of it as a process. An ongoing and never really finished process.

Even a fence can be very effective when done right.
On the border between South and North Korea and on river banks, etc., there is a double row of chain link fences, topped with razor wire. There are guard posts and lights. On freeway bridges, razor wire is wrapped around the supports to keep anyone from climbing the column and reaching the road surface from underneath.
It is ugly as anything, but it seems to serve the purpose of keeping the North Koreans out of South Korea. If North Koreans want to defect, they have to go through China.
The real fight is the incentives though. If people cannot find a good reason to come in, they likely will not come in.
That adds another 3.5 miles to the trip across.
News reports indicate that illegal immigration has dropped sharply since President Trumps inauguration, even though no progress has been made in building the wall.
http://www.powerlineblog.com/archives/2017/05/flow-of-refugees-slows-to-a-trickle.php
Original title says Refugees totally different unwanted set of free loaders.