A three-metre deep trench is being dug around Chad's capital, N'Djamena, to force vehicles through one of a few fortified gateways into the dusty city.
It appears the government is taking no chances against further attacks
It is one of the latest initiatives to prevent attacks from rebels based in the east of the country.
Last week, tree surgeons cut down centuries-old trees that lined the city's main avenue for fear they could provide cover for attackers.
The government beat off a coup attempt last month in a fierce two-day battle.
Correspondents say initial fears that the rebels would regroup and attack N'Djamena again have proved unfounded.
But it appears the government is taking no chances.
"It's part of our strategy," Interior Minister Ahmat Mahamat Bachir told Reuters news agency, without going into further details.
Last week, the government renewed the state of emergency imposed to restore order after the attack.
President Idriss Deby accuses Sudan of being behind the coup bid.
These charges are denied by Khartoum which in turn accuses Chad of backing rebels in Sudan's Darfur region.
The rebel attack took place just before the deployment of a European peacekeeping force to safeguard refugees from Darfur in eastern Chad and the Central African Republic.