It is really quite simple. The plan involves several regions or zones. These zones will be seperated by either a electric fence, moat, rivers of molten lava, or quicksand.
The first zone is simple. It will consist of rats and their corresponding fleas that will be infected with the plague. The intruders will not likely die while visiting this zone, but it will ensure that if they are not dominated by the remaining zones the chances of them making it to American soil will be slim to none.
Zone two will consist of hundreds of thousands of mockingbirds. Yes, that's right. mockingbirds. The mockingbird is very territorial. It dives and attacks intruders that come too close to its territory. They have even been known to attack their own reflections. In order to irritate the mockingbirds, automatic shakers will be placed on all of the trees. These tree shakers will knock the mockingbird young out of the trees as illegal aliens are walking by, sending the mother mockingbirds into an all out state of riot.
Zone three is the Chuppy zone. It is filled with Chupacabras. To put it simply, Chupacabras suck all of the blood out of your body through your neck. They are part of Latin American legend and the odds are very good that the thought of the Chupacabra alone will prevent most imposters from even attempting to come over.
Zone four is the Ron Mexico zone. It will have thousands of American Pit Bulls trained by Mike Vick himself. Pit Bulls are known for biting the faces off of children and leaving them lifeless. A large group of them acting as a unit could easily take down an elephant. I certainly wouldn't want to mess with a herd of these bad boys.
Any impostor who makes it this far deserves a treat. And they are probably very hungy after just working past molten lava, electric fences, quicksand, moats, the plague, mockingbirds, Chupacabras, and of course Pit Bulls trained by Ron Mexico himself. At this point Roach Coaches will be set up all along the border to reward hungry travelers. They will need to energy to take on what they will encounter next.
The final and most daunting zone is a triple threat zone. No human alive today can successfully make it through this zone. It consists of Trekkies, RPG Freaks, and Civil War Reenactors. The site of this zone will certainly convince any on comers that they made a huge mistake by trying to come to America. They will at this point attempt to cross back into Mexico, even though it entails going back through Zones 1-4.