Farmers in Wales are on the lookout this weekend for early warning signs of illegal raves planned for their land.
Police made 36 arrests at Betws Mountain, Carmarthenshire, in 2005
The August bank holiday is seen as one of the most likely dates.
Authorities in Pembrokeshire admit they were not properly prepared when more than 500 people overran farm land at Marloes during the weekend in 2003.
Police, council officers and land owners now hold contingency planning meetings and at least one large scale rave has been thwarted this summer.
Pembrokeshire Council's pollution control and licensing manager Gareth Watts said an illegal event had been planned at Barafundle Bay on the last weekend of July.
RAVES IN WALES
Aug 2003: Over 500 at Marloes Court Farm, Pembs, and police said there were so many they did not have resources to move them on
Aug 2004: Similar number gather year later at Whistling Sands, Lleyn Peninsula. One officer injured and six people in court.
May 2005: Over 300 people descend on Betws Common near Ammanford. Police make 36 arrests with clean-up costs described as "substantial"
He said thanks to early "credible information," routes to the award-winning beach were monitored and people turned away.
Mr Watts said mobile phones and text messaging made it easier for organisers to spread the word and numbers attending could quickly grow.
He said as well as noise and rubbish there were many safety issues.
Throughout this week planners have been contacting farmers and landowners, passing on advice and asking them to be vigilant.
"We are very much aware that this weekend is the time when people might come down to the county and spoil it for the rest," added Mr Watts.
On August bank holiday 2003, more than 500 people spent the weekend on land belonging to farmer Owen Morgan at Marloes.
He said it was highly organised with a huge sound system and stage, but he was left "powerless" to move them on.
The police and council came in for criticism at the time for not stopping the event, but Mr Watts said lessons had been learned.
"We were rather slow off the mark and it was perhaps a case of a lack of coordination between the different agencies.
Authorities say they prevented a rave at Barafundle Bay in July
"What we have done since is work with the police, farming unions, land owners and others to develop a protocol so we understand who will do what.
"It's not rocket science - it's just planning and being prepared to respond quickly - acting quickly is the key and being vigilant."
Rebecca Williams, Pembrokeshire executive officer for the Farmers' Union of Wales, said landowners were now more aware of the threat and what they should do.
"One of the main concerns is the rubbish - not just the cans and bottles but human waste," she said.
"It can cost thousands and thousands in clean up costs and if there is human waste then the land can be out of use for weeks.
"Farmers are being extra vigilant this weekend and our advice has been do not be afraid to report anything suspicious to the police."