Constable Lesley Eason, of Waikouaiti, said the move appeared to be aimed at motorists driving on to the beach at Blueskin Bay.
''I believe it has been deliberately put there. There have been some people who are not very happy with people taking their vehicles on to Blueskin Bay, local people,'' she said.
There had also been a report of broken glass found scattered in the same area last year, she said.
The latest discovery was a concern, particularly given the beach remained busy at this time of year.
''I believe it's put there more for vehicles, not for people, but the fact is it could hurt a person, especially at this time of year when you've got kids and stuff running around in bare feet.''
Police inquiries were continuing and Const Eason said she would be speaking to ''a few'' people in the coming days.
More than 60 pieces of rusted barbed wire were found in the sand earlier this month.
