Drug traffickers have become increasingly crafty over the years. Using methods like mules, planes, and even submarines, they have been finding new ways to evade authorities in order to expand their drug enterprise. Now, it looks like they have enhanced their methods once again.

Investigators say they have uncovered a cross-border tunnel in Calexico, Calif., linking to a restaurant in Mexicali, Mexico, that smugglers have been using to peddle marijuana between the two countries. The building of cross-border tunnels shouldn't come as a surprise, but the precautions that the smugglers took to hide it certainly should. They purchased the piece of land where it resided and built an entire house around it - the first time such an instance has occurred.

The tunnel was quite expansive, measuring about 415-yards, or about four football fields, and utilized a rail system, along with lighting and electricity. However, the real highlight of the discovery was the land and house that was used to conceal it. The land was purchased for $240,000, while the three-bedroom house it was built on cost $86,000.

This investment illustrated just how confident the smugglers were in their operation, but unfortunately for them, their expectations didn't pan out like they had hoped.

"I continue to be amazed by the ingenuity, the tenacity and the stupidity of people who dump so much time and money into a hole in the ground - seemingly unconcerned that they are doing so right under the noses of law enforcement," said Laura Duffy, U.S. attorney for the Southern District of California.

"For the builders, the financiers and the operators of these sophisticated tunnels, there is no light at the end of the tunnel. We will seize your drugs and your tunnel before you even have a chance to use it." 

The raid didn't cover just that house, either. Another residence where the traffickers would stash the drugs, as well as a warehouse, were also raided. Four people were arrested on various drug trafficking, money laundering and tunnel-related offenses.

All in all, agents found 3,000 pounds of marijuana with a retail value of $6 million in the operation.