It's a frightening scenario: A huge boulder, suddenly and without warning, crashes onto a homeowner's property.

On O'ahu, it happens frequently enough to raise difficult questions: Who is responsible? What should be done to protect homeowners, and who should pay for it?

For those who are the victims of these random, potentially deadly incidents, the answers don't come easily.

The responsibility of preventing disaster must be shared, among homeowners, landowners, government agencies and developers. Each bears some responsibility in working to protect against potential disaster.

As natural erosion persists, rocks will continue to tumble, putting residents at risk of injury or death and property owners at risk of lawsuits.

Most recently, two boulders came down in a Niu Valley neighborhood in a two-week period earlier this month. In March, a boulder three feet in diameter rolled through a Palolo Valley house. In 2002, two Dumpster-sized boulders forced 26 Hawai'i Kai families to evacuate for 11 months. That same year, 26-year-old Dara Onishi was killed when a 5-ton boulder crashed into her Nu'uanu bedroom.

It's clear that preventative measures should be taken across the board.

Residents living in risky areas are not powerless to protect themselves. They can request that landowners whose boulders pose a potential hazard assess the situation and provide mitigation, if necessary. Those methods could include breaking up large boulders with expansive grout, netting and cabling, or fencing.

Development can also be more strictly controlled. The city, which issues construction permits, can require developers to conduct more rigorous geological assessments of potential hazards, disclose them to current and future homeowners, and provide effective mitigation.

Owners of sloping properties that contain potential hazards should survey their land and act accordingly. Remaining in ignorance as a legal protection is simply irresponsible.

Surveys and mitigation measures, while potentially expensive, offer the best course to making sure hillside homeowners and their neighbors reside in safety.

And when all parties work together, that goal becomes all the more attainable.