LOS EBANOS, Texas — All along the winding Rio Grande, the people who live in this bustling, fertile region where the U.S. border meets the Gulf of Mexico never quite understood how Donald Trump’s great wall could ever be much more than campaign rhetoric.

Erecting a concrete barrier across the entire 1,954-mile frontier with Mexico, they know, collides head-on with multiple realities: the geology of the river valley, fierce local resistance and the immense cost.

An electronically fortified “virtual wall” with surveillance technology that includes night-and-day video cameras, tethered observation balloons and high-flying drones makes a lot more sense to people here. It’s already in wide use and expanding.

If a 30- to 40-foot concrete wall is a panacea for illegal immigration, as Trump insisted during the campaign, the locals are not convinced. And few were surprised when the president-elect seemed to soften his position five days after the election, saying that the wall could include some fencing.

“The wall is not going to stop anyone,” said Jorge Garcia, who expected to lose access to most of his 30-acre riverside ranch after the U.S. Border Fence Act was enacted a decade ago.

Under the law, 652 miles of border barrier were built, mostly in Arizona. The 110 miles of fences and fortified levees that went up in Texas are not contiguous but broken lines, some as much as a mile and a half from the river.

Eight years after government surveyors marked Garcia’s land, he and his wife, Aleida, are still waiting to see if the Border Patrol will sever their property.

“This lets me know that whenever they want to build the wall, they can,” said Aleida, holding up a tax bill that shows the nominally expropriated sliver of property.

If a fence or wall goes up, the couple will be paid $8,300. So far, the Garcias and the rest of the village of Los Ebanos have been spared because the erosion-prone clay soil is simply too unstable, she believes.

Geology conspires against wall-building up and down the Rio Grande Valley. So does a boundary water treaty with Mexico and endangered-species laws. Catwalks and tunnels had to be built into existing fences to accommodate endangered ocelots and jaguarundi, two species of wild cat.

The gaps in the border barrier include an entire flank of the River Bend golf club and resort in Brownsville.