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 venues work together to support Vale Earth Fair
The weather has forced the special 50th-anniversary edition of the Vale Earth Fair to relocate.
Royal Guernsey goats on show at Government House
A late summer show featuring Guernsey's gorgeous rare breed goats is at Government House today (Saturday 29).
Grassroots Guernsey football clubs get matchday ball donation
Clubs competing in the Priaulx League will be kicking around professional-grade balls this season.
New operator sought for Guernsey's Digital Greenhouse
States say the Digital Greenhouse is best run by the private or voluntary sector.
One fifth of Year 1 schoolchildren in Guernsey overweight
Public Health say there's a 'sustained difference in weight status by school fee status' and that this is a worrying health inequality.
Sark Shipping told to get its finances in order
Chief Pleas has extended a £300,000 loan until November to prevent the government-owned company from going into default.
Reliability of Alderney airlinks to be reviewed
"Recent disruption" has prompted a review of air travel reliability to and from Alderney.
Guernsey's final summer show cancels the fireworks display
A heightened fire risk caused by the dry summer has led to the cancellation of the North Show fireworks.
