But one Chinese man succeeded at breaking through the security dragnet, protesting briefly in Ritan Park with his young son and a sign that read, “Shandong Huimin County government illegally sold my grandmother’s house and took away the money!”

Now, the family says, the man’s 73-year-old mother is being harassed by the police in retaliation. Their story is a slice of Beijing life that largely escaped view during the Olympic Games and a reminder of the surveillance that continues through the Paralympic Games, which begin Saturday.

“I really didn’t know my son was going to protest in Ritan Park,” Yang Guiying said in an interview last week in her modest apartment in Daxing, a Beijing suburb, as a uniformed policeman stood on the landing outside her door. She was already under police surveillance; the protest “definitely made things worse,” she said.

Yang suffers from a kidney disease and has difficulty walking without taking breaks. That did not stop state security from sending two plainclothes police officers to ride along with her on a public bus, with two marked police cars behind it, she said.

“I’m just an old lady,” a teary-eyed Yang said, wearing a worn yellow blouse and two layers of pants even in summer. “I’ve done nothing wrong.”

But a complaint she filed in 1990 is a thorn in the Communist Party’s side. Her parents’ property in Huimin county, Shandong province, was taken away that year by local government officials who built in its place a financial services center housing two banks. They failed to compensate the family, said Yang, who has a written acknowledgment from the local housing bureau recognizing her family’s ownership of the property.

Six years ago, Beijing’s Ministry of Construction urged Huimin county to solve the dispute. The local party secretary’s response was to recognize that the land had been private property and to offer the equivalent of $22,143 for it, the family said — that is about 3 per cent of what would be paid for a similar-size plot in some other rural areas.

He Siqing, the party chief, did not answer repeated calls to his cellphone. A woman at the Huimin bureau of letters and calls who gave her surname as Liu said on Monday that the county was willing to negotiate. “We’re working on it,” she said.

Yang’s son, Hai Mingyu, a Beijing-based graphic designer, said his mother had been warned before the Olympics not to cause trouble during the Games.

But then he heard about Beijing’s plan to set up the protest pens in three public parks. He decided to stage a protest there. Planning to bring along only his 3-year-old son, he said, he figured he did not need to formally apply for permission.

Of the 77 applications from 149 people that did get filed, all were “withdrawn” or rejected, according to city officials. Rights activists have criticized the pens as an empty and cynical gesture.

When Hai arrived at Ritan Park in downtown Beijing on August 9, he recounted, he noticed a group of foreign journalists taking photographs. As soon as he approached, a Chinese woman asked him where he was from and what his case was about. “It’s no use talking to these journalists,” she told Hai. “They are only here to report on Chinese culture, not protests.”

Shortly afterward, Hai began to speak with three foreign reporters, asking if they were covering human rights issues. The woman immediately barked an order into a cellphone and more than 20 plainclothes police officers showed up in seconds, Hai said. Bystanders spoke up for Hai, who had explained the case about his mother’s land. Police tried to take away the sign that Hai’s son held, but the crowd shouted at them to leave his son alone, he said. Police called for backup at the north gate. Hai, protected by the presence of foreign cameras, walked to the south gate and climbed into a taxi with his son. His protest lasted less than 10 minutes.