William La Jeunesse filed another fascinating report from the Mexican border, as he takes a week-long look at what the Border Patrol is doing to prevent illegal immigrants and smugglers from entering the United States. 

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On Monday, he reported from near Tucson, Arizona, where apprehensions of illegals have dropped immensely. He watched from the air as agents went after "spotters," who try to direct the flow of drugs across the border. 

Today, he reported from Yuma, Arizona, where they installed the "gold standard" of fences in 2008. Up to 800 illegals a day were being arrested in 2005, but today, the number is averaging around 15 a day.

La Jeunesse explained that it's actually three layers of fencing stretching across nine miles, with a 70-yard "no man's land" in between.

Some still try to climb the fences with a homemade ladder and rope, but few succeed.

The "floating" fence actually rises and falls with the sand. Before the fence was installed, it was common for smugglers to ride across the sand dunes in ATVs.

Now, 92% of those who try to cross in the Yuma Sector are apprehended, a Border Patrol official said.

The state-of-the-art fence has also dramatically reduced "banzai" runs in which large numbers of illegals attempt to overwhelm agents on the other side.

And it has allowed agents in the sector to focus more efforts on patrolling the Colorado River, where illegals try to swim across or walk across a bridge made out of sandbags. 

The issue of a wall at the Mexican border has been at the forefront of the Republican presidential race after Donald Trump vowed that, if elected, he would construct an impenetrable wall and convince Mexico to pay for it.

Agents say a fence alone isn't enough to solve the problems. They say if it's not properly defended, illegals will find a way to get through it. 

They also emphasize that those who are caught must be prosecuted and jailed in order to deter others from trying to enter.

See the report above and tune in for William's next report, tomorrow at 11a ET on "Happening Now," when he looks at the port of entry in San Diego.

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