A hole has appeared behind the end of the German wall at the eastern side of L'Ancresse, near the slipway.
The States of Guernsey has fenced the area off, and work will start next week to fill it.
Under the latest States resolution, Environment and Infrastructure are to keep repairing the crumbling World War Two defence work for a number of years.
A £150,000 repair plan was agreed in April.
Members of the public are being asked to avoid the area and not pass the barriers.
Condor to be rebranded as Brittany Ferries
It's been confirmed that Condor Ferries will be rebranded from next year as its majority shareholder Brittany Ferries.
Bid to buy Barclays' Sark properties falls through
The Sark Property Company put up £20M for the homes, hotels and land but this was turned down by the trustees of the late Sir David Barclay.
New political movement launches in Guernsey
The founders of Future Guernsey carried out research that they say shows Guernsey's current political system is failing.
