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.
Teen jailed for sending explicit messages to children
A Guernsey teenager who sent explicit messages to children under 10 has been jailed for nearly three years.
New website to catalogue Guernsey States work
A new website has launched to publish information and updates about the work of Guernsey’s parliament.
Guernsey swimmer plans to cross the Irish Sea for charity
A man who calls Guernsey home plans to swim 21 miles from Northern Ireland to Scotland.
Guernsey's diving platform to reopen
The diving platform at the Bathing Pools will reopen following a 'concerted effort from the community, government and the private sector.'
Further delay to opening of Guernsey's specialist care units
Completing remedial building work on the Critical Care and Post Anaesthetic Units at the PEH is over running by around nine months.
Guernsey’s Old Quarter becomes street art hotspot
Vibrant street art is being used as a catalyst for the regeneration of St Peter Port's Old Quarter.
Sark man jailed for trying to meet and sexually abuse children
A man living in Sark has been jailed for 12 years for multiple sexual offences against children, including travelling to try and meet and abuse them.
Missing Guernsey child found
Guernsey Police have confirmed the schoolboy who was reported missing since yesterday morning (24 June) has been found.
