Mexican seniors will make border fence obsolete.

The number of Mexicans coming to the US dropped 65% from 2006 to 2010 although US law didn't change.  (A million in 2006 became 400 thousand in 2010).
The recession in the US took some of the lustre off the dream: (Mexican Immigrants Stay Put in Hard Times, RAND Scientists Say)

But the big change is happening in Mexico itself. Foreign Policy reports,  a grey tsunami is sweeping the world and countries like Iran and Mexico that had the biggest increases in young people are going to have the biggest increase in seniors in another dozen years. (The UN projects that over the next forty years, more than half the population growth (58%) will be in the over 60 bracket and only 6% in the under 30 bracket.)

The demographic momentum that fueled huge flows of Mexican migration to the United States has waned, and will wane much more in the future. Already, the net flow of illegal Mexican immigration northward has slowed to a trickle. With fewer children to support and not yet burdened by a huge surge of elders, the Mexican economy is doing much better than in the past, giving people less reason to leave. By 2025, young people on both sides of the border may struggle to understand why their parents' generation built this huge fence.

It's already happening. The number of kids under 4 has dropped more than 400,000 since 1996.  As the number of seniors increases and the number of new kids entering the job market decreases, there will be more and better paid jobs for the Mexican worker.

Illegal immigration to the US is trending down now.

This was the situation in 1991.  The youngest group
is also the largest.

Here's where the Mexican population is today.
That baby bulge is already moving up and
over 60 is growing.

Here's where the Mexican population is heading.
Every five year age group from 10 to 55
will be bigger than the two groups under 10 years old.