The way you stop it is to bring Mexico's economy up to speed. Mexico should be a very rich country, so should Brazil and Argentina. The only non-basket case economy in Latin America is Chile. Of course the left in America will always bemoan the fact that purer than the wind driven snow marxist Allende, was overthrown by that mean old Pinochet who brought prosperity to Chile.
If this was a liberal discussion board you would be scolded. It is considered by liberals obligatory when talking about the overthrow of Allende by Pinochet to mention at least once- "CIA assistance"- in the Coup.