I see two issues here:
1. Look at the entire Gulf Coast of the US, that's where they will go via boat, if we build a wall. It will keep the USCG & Navy very busy keeping the boats full of Mexicans out. I would think the Pacific would have issues as well, but the Gulf Coast has many more places to beach a boat. (It seems to make sense even now, sounds like a good research project, I wonder how many boats are stopped now with illegal Mexicans)
2. Cuba and Venezuela would love to get another Hugo Chavez in place. I can almost guarantee that would cause either the massive immigration issues or possible US Military intervention in Mexico. If you really want to be scared here are some links on one of the Mexican Presidential candidates:
Info on Mexico City Mayor Andres Manuel Lopez Obrador (Best friend of Castro and Hugo):
Link: http://www.publiuspundit.com/index.php?cat=78
http://www.answers.com/topic/andr-s-manuel-l-pez-obrador
http://www.mexidata.info/id196.html
All this said I still think a wall is a good idea, we just need to understand it may be much more costly than what we are paying now.
"....it may be much more costly than what we are paying now."
How? Your logic does not consider the billions in costs that states pay to cover facilities for illegals. BTW, I am not even mentioning the educational freebies and entitlements that illegals get in many states.
At last, someone finally gets a grasp upon reality. Currently the CPB and ICE agents look the other way at the legal border crossings while the coyotes and smugglers bring in the truckloads. As a Texan, I know that it is a short boatride for anyone in the gulf to go either direction. The "build a wall" crowd do not realize that the freaking wall would have to be the entire coastline of California, across the southern states, the entire gulf, all of Florida, and up the eastern seaboard to Maryland. This would pose no issues to commerce, since we could put everything on airplanes.