Parks and open spaces across Bexley will be left open at night from September as the council looks to save £200,000 a year.
Residents have voiced concerns about the measures which see the contract with Ward Security terminated after 18 years.
Chris Boud, 63, of Little Heath Road, Bexleyheath, said: "I found out this last night and I think it is a deplorable decision.
"It needs to be brought to the forefront and something needs to be done.
"It is very worrying and I will be getting onto my councillor and sending a letter to the council.
"We have got nice parks across Bexley and I am particularly worried about Danson Park with its lakes and boathouse.
"We already have people riding quad bikes on Bursted Woods churning up the grass.
"My husband is a member of a local bowls club and we go all over the borough using the parks, this is just the wrong decision."
Gareth Bacon, councillor for environment and public realm, told News Shopper: "There are 104 parks and open spaces across Bexley and currently there are only 23 that are locked nightly.
"They are patrolled by Ward Security and that is the contract which has been terminated.
"It will save the council £200,000 a year. Our budget has been cut by one third from central government and more money has gone towards social services.
"This has been a difficult decision but we have had to take a good hard look at these cuts.
"There is currently no barbed wire or electric fencing on any of Bexley's parks so if people want to get into them they can if they really want to.
"This decision is not really going to make much difference but on the other hand I don't really want to be doing it."