Actually, a fence does not work 24 hours a day because an unpatrolled fence will be dug under, climbed over, broken through, etc. It might help but I suspect being caught and arrested or sent back by a human, is the surest deterrent.
It's a physical barrier that must be defeated. The deterent value is where it really pays dividends.
Now, the success rate of a Mexican wanting to illegally enter the US is most likely in the high 90s. For this high of a success rate, Mexicans are willing to spend their entire life savings and the health of their family to make the journey.
With a physical wall, the success rate would be 10% at best and that is being generous. With the odds so stacked against them, how many are going to take such a risk?
I am not expert in the realities on the ground so maybe you can help me here: When the BP catches folks and quickly sends them back to Mexico (I believe that that happens occasionally), don't they typically turn right around and cross again? I think it is obvious that they do.
I assume that they are turned over to Mexican authorities right at the border?? They aren't taken deep into the Mexican interrior or anything are they?
It looks to me like our policy of giving them a box lunch and sending them "in the direction" of home is no more than a minor inconvenience for them. Like being delayed by a flat tire.
Am I wrong about this???? Please....any barrier opponent, help me out here. (Do we fingerprint them and/or take a DNA sample before sending them home?)