PHOENIX - The head of a special legislative panel on border security wants to use some of the money contributed by people across the nation to build a border fence for invisible buried sensors instead.

Sen. Al Melvin, R-Tucson, said there are places where a fence makes sense.

But Melvin, who chairs the Joint Border Security Advisory Committee, said Wednesday that a physical barrier is not always possible or practical. And the issue, he said, goes beyond whether the federal government or private landowners will give permission.

One is the fact that Tohono O'odham tribal officials have balked at putting the kind of fences along their 75 miles of international border that would stop people from crossing. Instead, the tribe, which straddles both sides of the border, has agreed only to vehicle barriers.

"The cables are buried a foot underground," Melvin said.

"You can't see it," he continued. "But we can monitor it."

Melvin also said buried sensors would get around objections from environmentalists who do not want to disrupt animal migrations and have raised concerns about the effect of fixed fences in rivers and washes.

The idea comes as the tally of donations to the week-old fund to build a fence has surpassed $100,000. That includes $106,000 contributed online by 2,400 donors using their credit cards, with another 184 individuals sending more than $10,500 in the mail.

For the time being, those funds are simply going to accumulate until the committee decides where to build the first segment and exactly what form that will take.

Melvin said these sensors can be as accurate as sonar.

"When you're in a submarine and you're getting 'pings,' you can tell the difference between a passenger liner, an aircraft carrier, another submarine," he said. Melvin said it's the same here, with a human triggering a different type of signal than a rabbit or a cow.

Rep. David Stevens, R-Sierra Vista, a contractor with the U.S. Defense Department, said sensors can also be far cheaper than a fence.

Melvin put the price in the neighborhood of $20,000 a mile, far less than even the lowest estimate for a fence of $400,000 a mile, or the $3 million-plus per mile the federal government has spent.

For monitoring, Melvin hopes to link them to an existing state agency that is staffed around the clock, like the Arizona Counter Terrorism Information Center, where local, state and federal agencies share information they gather, or the state Department of Transportation, which maintains an operations center in Phoenix where staffers monitor the freeway cameras.