When Nora O'Brien hosts guests at the secluded Victorian farmhouse she has painstakingly restored, friends have been known to carp about the deafening chorus of summertime tree frogs.

"I've had dinner parties where people say, 'Can't you make them shut up?' " said the 49-year-old landscape company owner and mother of three.

But she and dozens of other families across the state are willing to put up with such inconveniences. For them, living rent-free inside a Maryland state park outweighs getting chased by skunks, startled by snakes or clearing horse droppings from unpaved driveways that double as public riding trails.

"We consider ourselves stewards," said O'Brien, who has lived inside Patuxent River State Park for the past 15 years.

She is among 43 resident curators in an unusual program run by the Maryland Department of Natural Resources in partnership with the Maryland Historical Trust. It is aimed at saving historic buildings the DNR acquired over the years as it purchased or accepted parklands that had houses, corn cribs and cabins on them.

In exchange for restoring the houses to rigorous national historic standards at an out-of-pocket expense that almost always reaches well beyond $100,000, the curators receive lifetime tenancy.

No rent. No property taxes. No condo fee. No new development to block the vistas.

Supporters say the program is a cost-effective way to preserve historic houses - three are on the National Register of Historic Places and the others are eligible for that consideration - without taxpayer dollars. The state would never have enough money, they say, to restore the neglected and dilapidated buildings.

State officials say curators have spent more than $9 million fixing everything from wood frame farmhouses to brick four-squares, based on self-reported expenditures and labor.

Curators not only brought the first indoor plumbing to some of the old houses, but paid tens of thousands of dollars to install wells and septic systems.

The finished products fulfill dreams of calling a piece of history their home, or saving a sliver of Maryland's past.

"It affords you the opportunity to have a very peaceful environment," said Leonard Mullar, who lives with his wife, Diane, in a house whose main section was built around 1801 in Patuxent River State Park.

Despite its 27-year history, the program remains little known and something of an oddity, drawing inquiries from other state and local governments grappling with preservation issues.

Christopher B. Summers, president of the right-leaning Maryland Public Policy Institute, wondered why any tenant would want to undertake such a costly agreement.

"I think it's a great deal for the state, but a lousy deal for the individual," Summers said. "Why would you make that investment? You get nothing out of it except a good feeling of living there."

Others question whether the properties should be returned to the tax rolls.

But the hardy group of curators - which includes a sound engineer, a librarian and people in the building trades - share an affinity for old houses and nature. They have the ability to look at a rotting house with buzzards and trees emerging from gaps in the roof and see a picturesque home enveloped in songbirds calling to their mates.

"You have to have a love for it to want to do it," said Kim Troiani, 32, who with her husband, Val, 29, became curators last year near where they grew up. "It's going to be a lot of work."

The Troianis recently removed 4 1/2 tons of debris from the 19th-century fieldstone house in the Fair Hill Natural Resource Management Area in Cecil County - a park Val calls his "5,500-acre backyard" as they embark on their huge undertaking.

The curatorship program started informally in the early 1980s when Agnes and Larry Bartlett grew horrified after learning that a deteriorating house they loved at the edge of Gunpowder Falls State Park was owned by the state, and was not for sale.

"I went down there and stomped my feet. I said 'This house is history,' " Agnes Bartlett recounted.

When the couple, now in their 80s, offered to fix it up if they could live there for free, officials' eyes widened.

The concept was a success, and has since become formalized.

Now, the state DNR lists requests for proposals on its Web site, hosts open houses to show properties, and enters into contracts with curators. Applicants have to show a five- to seven-year plan for restoration, and each contract is approved by the state Board of Public Works. The approval process can take a year.

Then comes the costly, hard work of restoration, with all structural changes subject to state approval.

Bob and Loreto Albiol - he's an anthropologist and she's a doctor - live in a house in Seneca Creek State Park that was built by Martha Parke Custis, granddaughter of Martha Washington. Bob Albiol estimates that refurbishing the 19th-century house, used as a quarry master's home, required an outlay of $250,000, not counting his labor - and he left his job as an assistant dean at Catholic University to finish it.

"If I included my time, it's over a million," he said.

And romance can hit hard against reality. Rains can wash out gravel driveways that the curators are not allowed to pave. It's up to them to shovel or plow snow from a half-mile-long entrance area. Some contend with frequent power outages. Maintenance is constant.

Not only could O'Brien not kill the groundhogs that devoured her Swiss chard, but the Mullars gave up maintaining a greenhouse because deer coveted everything inside.

"Sometimes they would actually crash through the glass there," Leonard Mullar said.

Children of curators grow up with a freedom foreign to their classmates and an insider's appreciation of nature.

Hannah Gonzales, O'Brien's daughter, was in grade school when her family moved to the park, where she and her brothers helped work on the house but also rode mountain bikes on park trails, jumped into swimming holes, fished, and waited in their cars while wild turkeys toddled out of their path.

Those experiences, and being rattled by condo living, led her and her husband, Rey, in their 20s, to become curators of a house near her mother's.

"We never had a reason to run away and play Huck Finn because the park was our lives," she said.

Mike and Brigitte Hisky live in Patapsco Valley State Park with their two teenagers.

"No one realizes what I mean until they see it. They are like, 'Where is everyone else's house?,' " said 14-year-old Gina Hisky.

"We go in the hot tub, at night you see the stars and everything. We scream. And no one can hear," Gina said.

Passers-by have been generally friendly. Plenty are lost.

"We are almost like the unofficial welcoming committee," Mike Hisky said. "People ask how to, how do you get to the river? They want to go fishing."

The state cannot find curators for all the houses it wants restored.

There's been no interest in a turn-of-the-century African-American schoolhouse in Fort Frederick State Park in Washington County, a small clapboard structure that sits on a half-acre near the park's maintenance complex; or for a little frame house in Doncaster State Forest in Charles County that was believed to have been used by the Civilian Conservation Corps during the Great Depression.

An open house in April for an 1810 house and outbuildings in the Grove Farm Wildlife Management Area in Cecil County drew just 10 visitors, a substantial drop-off from 75 the year before, and one proposal.

Bruce C. Alexander, who manages the program, suspects fewer people have the financial liquidity to tackle work that the state believes will require "a significantly greater investment" than the $175,000 minimum in the request for those proposals.

"I can only surmise that it was something to do with the economy," Alexander said.

The Troianis were discouraged by home prices in 2007, when Val's mother showed the couple a newspaper notice that the state was holding an open house at the Fair Hill property.

The couple was among five applicants. Their inch-thick proposal had photos of them working on their house in Aberdeen, and details down to the appearance of a garage they want to add.

When they first looked at the property, weeds and vines had grown two stories tall, sprouting through the sagging porch. Inside, the couple looked past holes in the walls and floors and saw the beauty in the hand-hewn beams and five fireplaces.

"We grew up in the woods. It's the best place," said Kim Troiani, who doesn't expect to be able to move in until next year. "We can fix up and restore this historic home and enjoy the property. Our kids will grow up in it. I think what you get back evens it out."

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