The drought that is burning up the American south-west is shrivelling the leaves on the Tisdales' trees. With their dwindling supply of well water, they may not be able to irrigate their crops later this year. The couple is fighting to block a giant landfill planned on the Indian reservation adjoining their land, while they do up old Ford Mustangs to make a little extra money.
But the Tisdales' main complaint concerns the streams of people whose footprints criss-cross their 280 acres - several hundred a week, they say - breaking fences, scaring cattle, sleeping under barns and bushes and leaving a trail of water bottles and rubbish. Along with a string of neighbouring ranchers stretching some 40 miles along California's border with Mexico, the couple say they are the new front line in America's effort to bar the door to illegal immigrants.
The railway line from San Diego to Arizona runs along the border, just south of the Tisdales' land. Scrub oak affords some shelter to migrants, in a countryside dotted with sage, buckwheat, yellow creosote bushes and jumping cactus. "We've always had light traffic," said Mrs Tisdale, whose farm fence is two miles north of Mexico. "One or two guys every other month. We would give them a sandwich and some water, and send them on their way."
Last year, however, the Border Patrol picked up 40 Nicaraguans on their ranch in a single night-time swoop. One night last week, with his dog "raising hell", her husband, a rancher since 1963, spotted the glowing cigarettes near the ranch house. "I let off a couple of rounds, and they lit off up the road," he said.
If the delegates at the Republican Convention this week should choose to take a tour of the border near San Diego, they will find an impressive barrier against unwelcome arrivals. A high steel wall snakes inland from the Pacific beaches. It has arc lights, foot and truck patrols and border guards with night-vision cameras reminiscent of Berlin in the bad old days. Fourteen miles inland, however, the wall stops, and the residents of the more sparsely-populated eastern half of San Diego County say the Clinton administration's Operation Gatekeeper, centred on keeping illegal immigrants out of the city itself, has merely shifted the flow in their direction.
Illegals, the "pollos" (chickens), are following their paid guides, the "coyotes", on gruelling trips of two and three days through arid, mountainous terrain away from the coast. The county borders Mexico for about 70 miles, but for more than half that length, about 46 miles, there is no real barrier - in some places vehicles can drive across. Eastern San Diego County, which used to see a tiny fraction of immigrant arrests, now accounts for a third, about 10,000 a month, and drug seizures have dramatically increased.
Spokesmen for the US Border Patrol say the change in strategy is deliberate. It used to be a short run from the edge of Tijuana to the San Diego suburbs, where arrivals could disappear in minutes. But in the Otay and Hauser ranges, where steep and rocky peaks reach 4,000ft, they can track the immigrants for miles and pick them up at checkpoints on back roads.
"What we call the window of apprehension is much larger," said a Border Patrol agent, Marco Ramirez. The rugged high desert, freezing winter nights and high heat in the summer were intended as a "psychological deterrent", he added, but they have proved much more than that. Among 25 Mexican migrants who have died in the area this year, the Mexican consulate in San Diego lists 16 who have died of exhaustion, exposure and dehydration.
On 2 July Virginia Manillo-Diaz, 34, was found dead of the "intense heat". On 23 July, Hector Torres, 23, from Guadalajara died after two days on the mountains. Earlier this month, south of the California border, the 48C heat claimed the lives of 11 Mexican soldiers in a motorised cavalry regiment who got lost.
Joe Lopez is a third-generation Mexican-American who ranches 80 acres on the slopes of Hauser Mountain. But he has little respect for the migrants who camp out by his spring. "To me they are trespassers," he said. "I don't care what race, what nationality." He has handed 54 people over to the Border Patrol, often at gunpoint.
Stories make the rounds of the ranches: the guard dog with its throat slit, the farmer who found two Mexican women breast-feeding five children desperate for moisture. The illegals are even blamed for a jump in the number of wildfires, fanned by the Santa Ana winds; five are believed to have died in one fire last year.
Local Republicans have accused officials of fudging the arrest figures to make Operation Gatekeeper look good. The Tisdales will lead a delegation of ranchers to San Diego this week to make their case, and have called for the National Guard to be brought in to boost the Border Patrol. "We send out troops to a foreign country to seal the borders," said Mrs Tisdale. "Why can't we take care of our own?"