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.
Guernsey's Water Lanes to remain uncovered
A planning condition for the new Les Ozouets campus has been removed after strong opposition.
Guernsey's greenhouse gas emissions fall
CO2 emissions are dropping, but the car and transport generally are consistently the biggest contributor.
Work on Guernsey's Victor Hugo Centre may begin by Easter '27
Progress is being made on the Victor Hugo Centre on Guernsey's seafront, after enough money has been raised to fund its capital costs.
Channel Islands mobile portability issues to be resolved soon
Problems exporting a JT number to the new Co-op mobile network should be over by mid-March.
Channel Islanders in the Middle East told to follow local warnings
As many as 94,000 British nationals either live or on holiday in places like Dubai which has been hit by Iranian missiles.
Freehold of Guernsey's Premier Inn for sale
The marketing agent says it achieves £753,000 rent each year and is promoted as a 20 year plus investment opportunity.
Unprecedented demand for cesspit emptying in Guernsey
Record February rainfall sees sewage carts carrying out hundreds more trips.
Food will not be exempt from GST in Guernsey
Deputies have voted through the concept of GST at 5% on food shopping - but were reminded the final vote is not until the summer.
