That's because a series of incidents — some fatal — have alerted the state and developers of the need to more aggressively prevent rockfalls in Hawai'i. The city also is taking action, and this year enacted stricter building-permit guidelines that require developers to complete an engineering slope hazard report when building on steep hillsides or on property adjacent to them.

"It's a new part of development for the industry overall to understand what steps one needs to take to develop on or near hillsides," said Micah Kane, chairman of the Hawaiian Homes Commission. When building in areas near slopes "we are taking a very intense review from a geotechnical standpoint as to how we are going to proceed near or even close to those lands."

The Department of Hawaiian Home Lands, which is planning to build about 3,500 new homes over the next several years, is taking a leading role in rockfall prevention.

"You hear on the news about rockfalls here and there," said Frank Makaawaawa, who lives on Kapahu Street in Kalawahine. "I think it is appropriate that these folks have come in. It is better to be safe than sorry."

Makaawaawa had landscaped his back yard around a large boulder. That rock and about 60 others on the hillside were considered to be extremely dangerous and likely to fall. A portion of the new quarter-mile protective fence will be directly behind his home.

"They said it had to go, and it was kind of hard for me to take," he said. "But I realized it is better to have the rocks go away than to go into somebody's house, or go into my house."

In recent years, boulders have closed roads and highways and fallen in residential areas, including in Kailua, Hawai'i Kai, Nu'uanu and Nanakuli.

A National Park Service ranger died in September when a boulder fell 40 feet and struck her as she was attempting to clear a rockfall on a remote East Maui road in Haleakala National Park. A Nu'uanu woman was killed when a 5-ton boulder crashed through her home in 2002.

Steve Martel, an assistant professor of geology and geophysics at the University of Hawai'i-Manoa, said Hawai'i's land has a high content of basalt rock, which tends to crumble with time. Fractures in the rock, coupled with the warm climate, abundant rainfall, vegetation and steep slopes all contribute to making the slopes suspectible to instability.

In Nu'uanu and elsewhere, residents have put up expensive rock-catching fences to try to protect their property. Others have hired consultants to survey the property above their homes and assess the potential danger.

The Navy is spending $225,000 to strap down a 60-ton boulder perched more than 100 feet above a private Moanalua Valley home after a survey of the property discovered the potential for it to fall. Navy Lt. Cmdr. Jeff Davis said the Navy did not want anyone to be hurt by a falling rock.

"That is what led us to getting the area surveyed and to act on this particular boulder," Davis said.

Don Metzger, who lives directly below the boulder with his wife and two daughters on Ala Lani Street, said one boulder fell onto his neighbor's lanai and others fall into the road regularly.

"I personally feel it is a very positive step, and we appreciate the concern on their part to get it done," Metzger said. "I couldn't do it. I'd have to get a contractor to go in there.

"When we have big rains, we do think about it. My wife will feel better when it is secure."

It can cost a homeowner tens of thousands of dollars to install a steel fence strong enough to hold back large boulders. But making O'ahu's roads safe will likely cost hundreds of millions of dollars.

Last year, a state Department of Transportation survey identified 66 highway sites on O'ahu that have a high risk of rockfall. Fifty-one other areas were rated moderately high. Cost estimates to mitigate the top 10 sites alone total $89.5 million.

The DOT already has spent millions to install rock catchment devices at Makapu'u and Waimea and to reshape the hillside at Castle Junction in Kailua.

Twenty-six families at the Lalea condominium project in Hawai'i Kai were forced to move out of their homes in December 2002, after boulders fell onto cars and buildings. Geologists determined the area was unsafe.

Developer Castle & Cooke and landowner Kamehameha Schools spent $5 million to have crews sweep the mountain of loose boulders and take other steps to make the condominium safe again.

Gino Merez and his family were forced to leave their Lalea condo and never returned. The family sold the condo and moved into a larger home atop Mariner's Ridge.

"Before we moved in, we noticed a few rocks that looked like they were teetering," Merez said. "Castle & Cooke told us what they had done and said no rocks had fallen into the units against the mountain. I didn't think at the time that was adequate."

Merez has returned to look at the mitigation work, and he said they seem to have done a good job.

"Anytime they do take measures to keep the rocks from falling is good," Merez said. "The Lalea situation sort of gave notices to these developers about their responsibilities or liabilities."

Harry Saunders, president of Castle & Cooke Homes, said the company has learned from the experience and has adjusted how it plans projects.

"There is a new awareness of rockfalls, and I'm really happy to see many developers are aware of it," he said. "You make modifications and take the extra steps. At the end of the day, no developer wants to see his customers hurt."

The design of the company's housing project in Makakilo was changed to make the project safer after the Lalea events, he said.

In May 1999, eight people died and 50 others were injured in a rockslide at Sacred Falls on the Windward side of O'ahu.

Attorney Arthur Park, who represented the families of those killed, said the Sacred Falls incident may have opened the eyes of developers that rockfall mitigation work is a not a luxury.

"I like to think maybe the consciousness has been raised by what happened at Sacred Falls, and property owners are trying to avoid death and serious injury," Park said. "That is not a good thing to have on your conscience. I hope that is what is motivating them more than just risk of liability."