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 businesses encouraged to use the daily St Malo ferry for European imports
The Chamber of Commerce will advise Guernsey businesses how to go about importing a range of French goods.
Guernsey's airline to drop its European holiday routes
Aurigny will concentrate on its new lifeline routes, existing UK destinations and an extra Paris flight.
A total ban on disposable vapes in Guernsey and Jersey is poised to take full effect
Disposable vapes will be outlawed from Saturday 31 January in a bid to stop the harm they cause to people and the environment.
Guernsey's Air Display to remain an early evening event
Organisers say last year's trial was a success and as a result the 2026 air display will begin at 6.30pm on 9 September.
Disgraced Guernsey politician and pastor jailed for 9 years
Disgraced Guernsey politician Jonathan Le Tocq will be imprisoned for 9 years for sexual offences.
10,000 LEGO brinks needed to build memorial bench for Guernsey boy
The Priaulx Premature Baby Foundation wants to honour the late Matthew Girard with a life-sized LEGO bench at his former primary school.
Former Island FM and Guernsey radio star dies
Tributes are being paid to John Randall, an early Island FM presenter who has died aged 68 after a short illness.
Storm Ingrid halts Guernsey charity sleep-out
Heavy rain and strong winds from Storm Ingrid have forced the organisers of a sponsored sleep out to postpone.
