Worked pretty damned well for China and (unfortunately) East Germany. Or are you denying historical fact? The San Diego fence GREATLY reduced crossings there as well. The Israeli fence reduced terrorism significantly.
The green zone in Iraq? Go back to the WW2 era and look at the barbed wire and ‘fencing’ on battlefields. Can you think of a reason it was there in use? There are a million legit reasons to build a fence and NONE to not do it.
Fences have worked since their creation and just because Rick Perry is AGAINST THEM that has no bearing on their historic effectiveness.
Two words: “Force multiplier”
Foolproof? No. So build it and back it up with patrols, cameras, GP Sonar, Predators etc. But a secure fence is absolutely a cornerstone of securing our border.
Only when manned with troops with orders to shoot to kill.