Marijuana in gas tank

SAN YSIDRO, Calif.--It's probably the busiest border crossing in the world, and every day, mixed in with the thousands of law-abiding people coming into the U.S. here from Mexico, smugglers attempt to outfox the law and sneak in all kinds of contraband -- like 38 pounds of marijuana hidden in wrapped packages found inside the gas tank of a car on Monday.

From pot to meth, cocaine to hidden illegal immigrants, the list of things that are smuggled in is long. And that's before you even start talking about stopping terrorists from getting into the country.

For U.S. Customs and Border Protection (CBP) officers, stopping the illegal activity is a never-ending battle, even as they attempt to make passage as fast as possible for everyone else.

To help them do their jobs, they have a slew of different technologies at their disposal -- and some very low-tech tools as well. As part of CNET Road Trip 2012, reporter Daniel Terdiman stopped in at San Ysidro to see what CBP is throwing at the problem.