For five years, Michael and Linda Sandler treated the back yard of their Silver Spring house like, well, their own back yard. They cut the grass, built a small flower bed, enjoyed the usual domain over their little patch of suburbia.

Then came a letter last February from Montgomery County officials telling them that by mowing their grass, they were breaking the law. Their raised garden bed would have to go, along with Mike's portable basketball hoop, a canoe and about 100 square feet of their asphalt driveway.

Almost all of their back yard, the letter said, was part of a forest conservation plan agreed to by the property's previous owner. An ironclad addendum to their deed, attached for perpetuity, forbade them to mow, dig, erect fences or pull weeds. The land was legally required to revert to its wild state.

The couple says it was all news to them.

"We were in shock," said Linda Sandler, standing in the roomy house on Timber View Court near the intersection of Kemp Mill and Randolph roads. The dining room table was covered in documents, including one that hits them with a $2,500 fine. "It was the first we'd heard of it. I didn't even know what a conservation easement was."

A year later, the Sandlers and three other families on their block remain caught in a bureaucratic tangle that is becoming more common as the county's booming growth pushes farther into environmentally sensitive areas.

"There are more and more properties encumbered with these easements, and we're seeing more and more violations," said Michele Rosenfeld, a former park and planning lawyer who now represents homeowners who find themselves on the wrong side of the easement law. "Sometimes they knew about the easement, sometimes they didn't."

The county oversees almost 2,500 conservation easements on private property. Planners now routinely require them when landholders seek to subdivide properties close to stream beds or established forests, a practice that has become increasingly common in booming Montgomery.

With the growth in easements has come a surge in complaints. The Sandler family was one of 78 owners cited by the county for easement infractions last year, up from 26 in 2004.

The Sandlers say they were never told that the lot they bought in 2003, which slopes down to a stream called the Northwest Branch, carried such strict protections. They didn't pay much attention to the deed or the official plat, both of which describe the easement.

The Sandlers did find a paragraph in their contract that indicates their property includes "land dedicated to a conservation easement as part of a Forest Conservation Plan." That paragraph is checked "Yes" and the Sandlers' signatures are on the form. But Michael said they read right over it in the flurry of signing dozens of closing documents.

"It's this little thing hidden in there," said Michael, a financial planner. "Listen, we wouldn't have bought the place if we knew we couldn't use the back yard."

Planning officials say they can't be present at, or even aware of, every real estate closing. Under county law, a property's seller is responsible for disclosing the existence of a conservation easement. And the buyer, the moment he or she becomes the owner, is on the hook for maintaining it.

"We usually hear from them, unfortunately, after they've built their pool," said Cathy Conlon, a supervisor in the planning office. "We've been preaching for years to the real estate agents to be more forthcoming with buyers and to encourage them to contact us."

In recent years, the agency has launched an effort to inform people about the easements, including a new Web site that shows easements for every address in the county. Since 2009, the county has taken to sending owners notices of violations, withholding penalties if the infractions end.

"Our goal is compliance, not collecting fines from people," said planning department spokesman Valerie Burton.

The easement covering most of the Sandlers' back yard was created by the previous owner, Mervin Yetley, who had a single house on a very large lot. In 2003, the county approved Yetley's request to subdivide his land on condition that an easement area running along the back of all five lots was allowed to grow as undisturbed forest, forever.

The Sandlers bought one piece of the property and immediately joined the other four buyers in signing with a builder to construct the homes. Neither Yetley nor the builder mentioned the easement, Michael said.

Yetley, who moved to Upper Marlboro, did not return several messages. But the builder, Mautaz Ezzat of Gaithersburg, said all the buyers knew about the conservation plan, or should have.

"Absolutely, they knew," Ezzat said. "I was aware there was an easement in the back of the property and I have no doubt they knew about it."

Ezzat said all of the buyers came to a meeting to pick colors and review plans for their new houses. All of the plans showed the easement, he said, although he could recall no other specific conversations about the protected area.

Sandler said he never heard a word about the easement.

"All of these people were aware of the easement, but they didn't tell me about it?" he said. "They all made a lot of money off of the deal."

The Sandlers' next-door neighbor, Yemi Fashima, has less of his yard covered by the easement but still faces a $1,000 fine for mowing the area and other infractions. He said he was aware of "some kind" of conservation area, but thought it was a much smaller one defined by a silt fence that was erected closer to the stream during construction.

"I had no idea that I couldn't cut my grass," Fashima said. "The county had people out here multiple times when the houses were being constructed. They saw the builder putting down the grass. Why didn't they say something then?"

Conlon said her agency's four full-time inspectors visit every site at least twice during construction. But they depend on builders to notify them when the work wraps up, something that doesn't always happen. Building inspectors from other agencies don't usually include easement issues in their property reviews, she said.

"Some are better than others," she said.

Conlon said planners are now less likely to approve plans that place homes too close to conservation areas. When possible, the county now tries to keep easement lines off individual lots. And the county now requires conservation areas to be posted with signs that prospective buyers would see as they house-shop.

"The environmental reviews are definitely more attuned to what is realistic based on our experience," Conlon said. "We try to make sure the easements are drawn in such a way as to work with homeowners, and not be in conflict with them."

The Sandlers say that is all too late for them. They are appealing an administrative judge's ruling against them. Michael said the flap is costing him sleep.

"The county is going solely by its code, and they don't care if it's destroying people's lives," Linda said.