They call it monkey herding: stationing a specially trained guard at a hot spot to shoo monkeys away from residential areas. The guard may tap a stick, an umbrella or a net on the ground, or just tell the monkeys to go away.
This is a method wildlife rescue group Animal Concerns Research and Education Society (Acres) is proposing to the authorities to deal with monkeys in residential areas.
This has become such a big problem that the authorities last year culled about 570 monkeys, or nearly one-third of the estimated 1,800-strong local population.
But groups such as Acres have called for alternative ways to deal with the problem.
Acres has been conducting studies on the herding method for a year. It carried out two trials in Bukit Timah and Bukit Batok in August and September.
The results were promising, with monkeys no longer entering residential premises as often as before, said Acres' macaque rescue team and campaigns executive, Ms Sabrina Jabbar.
But more manpower and funding will be needed to continue such efforts and conduct further research, she added.
"By tapping the object on the ground or pointing it towards them, the monkeys naturally understand that it's harmful and move away," said Ms Jabbar, who stressed that herding should only be done by trained professionals.
In both projects, she was the only monkey guard, though there should be two or four ideally, said Ms Jabbar.
Acres hopes to raise at least $10,000 to continue its efforts and to hire four staff members.
Acres chief executive Louis Ng said: "If we have more funding, we can expand the team and cover more areas."
He said four staff members, working in pairs and in shifts, would be a bare minimum.
The problem of monkeys disturbing residents has eased this year, going by figures from the Agri-Food & Veterinary Authority (AVA). It has received 520 pieces of feedback on monkeys so far this year, compared with 1,860 for the whole of last year.
About 150 monkeys have been euthanised this year.
An AVA spokesman said the deployment of guards may not necessarily resolve issues of monkey aggression or nuisance as "such monkeys, accustomed to being fed by humans, would likely continue to venture out of the forests to source for food from people".
The "indiscriminate release" of aggressive monkeys back into the environment "merely transfers the problem from one estate to the next", and relocation options are limited due to land scarcity, she said.
This is why euthanasia is AVA's "last resort", she added.
Mr Ng and other activists said there is a need to better educate the public on monkey behaviour, such as how certain gestures such as making eye contact with the monkeys will provoke aggression.
Residents should also not leave food lying around as this is what lures monkeys into their estates. All of the calls Acres received about monkey nuisance involved residents not disposing of their trash properly or leaving food out in the open.
Ms Jabbar said one advantage of monkey herding is that it serves an educational function. "Residents and security guards can observe that monkeys aren't aggressive creatures if you know how to relate to them."
Assistant Professor Michael David Gumert of the Nanyang Technological University's School of Humanities and Social Sciences said that while herding can be costly and labour-intensive, it is worth it.
Monkey guards can be "chaperones" to warn residents or passers-by if their interactions with the monkeys may provoke aggression, said Prof Gumert, who studies long-tailed macaques here.
Bukit Timah resident Benjamin Ng agreed that more public education is needed.
The 66-year-old retiree, who lives at Springdale condominium, said: "I don't think you need to kill the monkeys."