India is constructing a fence along its entire border with Bangladesh in an attempt to keep out tens of thousands of illegal immigrants. But the fence project has been bad news for many living along the border.
Lt Col Lutfur Rahman was worried about my safety.
For the Bangladesh Rifles, guarding the border between two ostensibly friendly neighbours is no ceremonial duty.
Around 25,000 men are fanned out along the frontier on the Bangladeshi side, and they speak of the Indian Border Security Force as if it were an enemy.
"Don’t stray off this road, that is where India starts," said Lt Col Rahman, pointing with his silver-tipped swagger stick at the ground a yard from our feet. "They may shoot, they are so brutal."
The fence being built by India around Bangladesh is creating tension in places, and occasionally there have been exchanges of fire.
The patrol had begun at dawn, when the fog from another chilly night still clung to the trees of the mango orchards.
The Bangladeshi sepoys walked in single file 10 yards apart, their rifles at the ready.
They moved stealthily, the silence broken only by the squeak of boots and the soft clanking of equipment.
They were alert despite the early hour.
Sometimes when there was a gap in the mist the shadow of the fence could be seen over in India.
It was made of wire, 12 feet (3.6m) high, and stretched out in a straight line across the fields to the horizon.
Bicycle rickshaws drifted along a raised road behind it, and every so often the silhouette of an Indian border guard stood out in the fog.
Bangladesh has no objection to the concept of a fence.
The issue is where exactly it should be.
Bangladesh says a 30-year-old accord, drawn up shortly after the country became independent, means no barrier should be built within one 150 yards of the actual frontier, which is marked by triangular concrete pillars.
Along much of the route India is keeping the fence well back inside its territory.
But it must run through wetlands, jungle and hills, as well as heavily populated areas.
And in some places the accord is being violated, complains Bangladesh.
India is well on the way to finishing this massive project.
The border is 2,500 miles (4,000km) long.
India’s parliament has been told work to seal it will be completed by the end of this year.
There will be floating observation posts in the region’s many rivers.
The aim is to stop illegal migration – Delhi has claimed there are 20 million Bangladeshis in India illegally.
Security at a price
And there have long been allegations too that Indian rebel groups fighting separatist insurgencies in the north east find sanctuary in Bangladesh, something Dhaka denies.
The trunk of this big banyan tree is in India. But if you stand here, under the branches, you are in Bangladesh
But India’s extra security is coming at a price – and its being paid by the Indians whose fields and houses butt right on to the border.
As the work continues they are finding themselves on the wrong side of the fence, in a narrow strip of land between Bangladesh and the barrier.
The difficulty for me was getting to talk to them.
I was on the Bangladeshi side and could not cross legally.
Everyone knows exactly where the frontier lies in such a place.
Sometimes it is a matter of life and death – we had met several Bangladeshis with scars from bullet wounds.
They claimed they had innocently strayed into Indian territory and been shot at.
"The trunk of this big banyan tree is in India. But if you stand here, under the branches, you are in Bangladesh," said a helpful bystander.
The first huts of the Indian village of Shosani were on the other side of the tree.
I managed to call out to headman Dinea Singha.
We met on the frontier, at the spot where the buildings and the mist meant we were out of sight of the guards on the fence, 150 yards further into India on the other side of the village.
It was all a bit furtive.
Dinea Singha’s name means Lion of the Day but he was nervous as a kitten.
He told me the fence was making the lives of the villagers much more difficult.
There were gates but they were not open all the time.
They had begged for the barrier to be put on the actual border line, he said.
But now they felt as if they had been fenced out of their own country, he added.
As we were talking I noticed the Indian villagers sitting nearby watching us were beginning to get up quietly and sidle away.
Someone said the Border Security Force was coming.
Dinea seemed to be genuinely frightened of his own country’s border guards.
Within the lifetimes of the oldest villagers India and Bangladesh were part of one country.
The border was drawn on the map by a British bureaucrat, but now it is being fortified with steel.
Dinea quickly fumbled to take off the microphone I had clipped to his shirt, dropped i
t on the ground and scurried away.
When he was a short distance from me he put his hands in his pockets and sauntered off in the manner of a schoolboy leaving the scene of a misdemeanour trying to pretend he had never been there at all.