I don't know what your approach is in totality, but it doesn't make sense to me as you've explained it.
A fence won't cause problems with legitimate business unless you can tell me what legitimate business crosses the border without our knowledge. Are GM vehicles on trucks doing the Rio Grande crossing on paths we haven't monitored?
It's not Mexico's job to guard its border, no more than it's our job to prevent felons here from sneaking into Canada or Mexico. Putting the blame on them for our stance that keeping them out is too costly is ridiculous.
If they don't care about their northern border, that's their choice. If we don't care about our southern border, that's our choice. Sounds like we're starting to care, but your assertions are definitely extremist at present. I hope you rethink them.
"ARTICLE VIII.
The Mexican Government having on the 5th of February, 1853, authorized the early construction of a plank and railroad across the Isthmus of Tehuantepec, and, to secure the stable benefits of said transit way to the persons and merchandise of the citizens of Mexico and the United States, it is stipulated that neither government will interpose any obstacle to the transit of persons and merchandise of both nations; and at no time shall higher charges be made on the transit of persons and property of citizens of the United States, than may be made on the persons and property of other foreign nations, nor shall any interest in said transit way, nor in the proceeds thereof, be transferred to any foreign government.
The United States, by its agents, shall have the right to transport across the isthmus, in closed bags, the mails of the United States not intended for distribution along the line of communication; also the effects of the United States government and its citizens, which may be intended for transit, and not for distribution on the isthmus, free of custom-house or other charges by the Mexican government. Neither passports nor letters of security will be required of persons crossing the isthmus and not remaining in the country.
When the construction of the railroad shall be completed, the Mexican government agrees to open a port of entry in addition to the port of Vera Cruz, at or near the terminus of said road on the Gulf of Mexico.
The two governments will enter into arrangements for the prompt transit of troops and munitions of the United States, which that government may have occasion to send from one part of its territory to another, lying on opposite sides of the continent.
The Mexican government having e agreed to protect with its whole power the prosecution, preservation, and security of the work, the United States may extend its protection as it shall judge wise to it when it may feel sanctioned and warranted by the public or international law."
Treaties over-ride popular opinion. Sorry.
http://www.yale.edu/lawweb/avalon/diplomacy/mexico/mx1853.htm