Huynh Ngoc Chenh (C), holding a sign which reads "Protecting the environment is more important than economic development" stands with protesters during a demonstration demanding cleaner waters in the central regions after mass fish deaths in recent weeks, in Hanoi, Vietnam

Vietnamese blogger Huynh Ngoc Chenh sneaked out through a back door and reappeared the next day in a public square to hold a one-man, anti-government protest.

But having been given the slip once, police wasted no time in nabbing him after only five minutes.

It was one of many free-speech experiments squashed by Vietnam’s communist government, underscoring the dilemma U.S. President Barack Obama has ahead of a visit on Monday in which human rights will be central to decisions about how far Washington is willing to engage its former enemy.

Unlike many dissidents, he was not arrested for Sunday’s demonstration in Ho Chi Minh City, which got him 12,000 Facebook “likes” for making a stand against what he calls an endemic problem of abusive police.

There are six men watching my house right now,” said Chenh, 64, who was escorted home and told to stay there.

Sometimes, they stop me from leaving, other times they let me go out but they follow me everywhere.”

His sit-in came as rights groups and activists accuse police of using heavy-handed measures to stop protests held in cities the past two Sundays to demand government answers over an unexplained environmental disaster that caused mass fish deaths last month.

The timing of protests could not be worse for Vietnam. The White House on Thursday said Obama was still grappling with a decision on whether to lift a lethal arms embargo on Hanoi, one of the last vestiges of the Vietnam War.

Vietnam wants closer military ties and access to U.S. defence technology as a deterrent against Beijing’s assertiveness in the South China Sea, over which the neighbours are bitterly at odds.

Though that fits in with the U.S. strategy of containing China, Vietnam’s jailing and intimidation of dissidents remains an obstacle to Washington’s push to turn its former enemy into its newest Asian ally.

Obama’s top Asia adviser Daniel Kritenbrink on Wednesday told reporters that “human rights would be a key factor in whatever arms sales decisions we may or may not make“.

Kritenbrink also said “Obama will not try to duck the issue. He is expected to meet dissidents and will address human rights in Vietnam both publicly and in private”.