MISSION, Tex. — Along the Rio Grande here, the suspected smugglers trying to slip into the United States have certainly noticed their adversaries on the water: burly commandos in black-and-white boats mounted with .30-caliber machine guns and bulletproof shields. The patches on the officers’ camouflage fatigues identify them not as federal Border Patrol agents but as another breed of law enforcement entirely.

Texas game wardens.

A team of them — whose routine duties include investigating fishing tournament cheaters and making arrests for B.U.I., or boating under the influence — patrol the Rio Grande, pulling smuggling suspects from the river and dodging rocks thrown from the Mexican side. Members of the Texas Rangers have also traded in their familiar white cowboy hats for camouflage so they can blend into the brush on covert nighttime operations.

On the border, Texas uses helicopters with infrared technology. It monitors motion-detecting cameras it installed on private ranches. And rather than rely on federal high-altitude surveillance airplanes, Texas bought one of its own, for $7.4 million.

Gov. Rick Perry’s recent announcement that he was deploying 1,000 National Guard troops to the border has generated widespread attention. But it was only the latest step in a broader, decade-long strategy by Mr. Perry and other Republican leaders to patch together Texas’ own version of the Border Patrol on its 1,200-mile border with Mexico.