SELLS, Ariz. —  Each day, at least 1,500 illegal Mexican immigrants cross a makeshift border into southern Arizona’s Tohono O’odham Indian Nation (search).

Tribal Police Chief Richard Saunders is responsible for the area the size of Connecticut, and in March alone his officers and federal Border Patrol (search) agents captured more than 16,000 illegal immigrants. But at least that many got through without being detected.

Illegal immigration isn’t the only issue for Saunders’ small force, which also has to police the drug trade.

So far this year, nearly 20,000 pounds of marijuana and an unspecified amount of narcotics have been seized. Agents believe that’s just a small fraction of what’s getting across the border.

The tribe is currently spending half its federal money on border security, instead of on housing, roads and schools.

Crackdowns in other parts of Arizona, New Mexico and California have left this 75-mile border on Native American land wide open. The 69 police officers and few border agents just aren’t enough to stop the flow of people coming in.

Tribal leaders say they’re badly in need of more officers, vehicles and other resources in order to control the overrun border.

Click here to watch a report by Fox News Channel's Adam Housley.