They have to be guards, teachers and racers. These are the different hats worn by Police Coast Guard officers, who help keep Singapore's coastline safe.
Last year, 15 vessels were caught intruding into Singapore, down from 18 the year before. In 2011, 13 were seized.
The marine police also keep a lookout for people entering Singapore waters illegally or trying to do so. Last year, 49 were caught, while in 2012 there were 41. In 2011, 54 were apprehended.
But the island-state's geographical location and busy ports make it difficult to secure sea borders.
Superintendent Tan Tian Yeow, head of operations and security for the coast guard, said: "Unlike in the air or on land where traffic can be funnelled to checkpoints for checks, the coastline is porous, presenting numerous vulnerable points."
Currently, 63km of Singapore coastline is guarded by floating sea barriers, land fences and sea fences.
The longest stretch of floating sea barriers is a 5km one in Pasir Ris. These are used near recreational areas as they can also act as safety barriers for swimmers. For land fences, which are about 2.5m tall, the longest stretch of 6.8km is in Tuas South.
An extra 30km in barriers will be added by 2019, with another 50km more in the works. This means that 143km, or 74 per cent, of the 193km coastline will be barricaded.
Just like neighbourhood crime watch groups, there is a fish farmers watch group in the northern Singapore Strait roped in to look out for suspicious activity. Coast guard officers visit the group regularly to update and teach the members about what to look out for.
Despite the efforts, smugglers still try different ways to get through.
Sergeant Edward Cheng, 31, once discovered a large amount of contraband cigarettes of many brands hidden in bushes during a 12-hour patrol shift last year.
There were so many cartons that Sgt Cheng, who joined the force nine years ago, had to call a few colleagues to help him remove the illegal items.
In a border breach on Aug 19 this year, a 30-year-old woman hired child abduction recovery specialist Adam Christopher Whittington, 38, to snatch her two-year-old son from the parents of her divorced Singaporean husband and take him back to London. The two, along with Australian skipper Todd Allan Wilson, 39, sneaked into Singapore in a catamaran via Raffles Marina. All were arrested and jailed for 10 to 16 weeks.
Another challenge for the coast guard is to check for the illegal sales of marine gas oil. Since last year, 55 foreign crew members and three Singaporeans have been arrested for such sales. More than $22,000 in marine gas oil was seized.
Marine gas oil can be found in vessels with extra tanks, portable pumps and hoses, as well as complicated piping in the engine room.
As part of their job, coast guard officers sometimes have to chase illegal immigrants or smugglers in boats or "play hide-and-seek" with them - made trickier by the darkness and crowded sea space due to Singapore's busy ports.
Sgt Cheng said: "Patrolling might seem the same every day but it's not. You don't know what to expect and you have to be ready for anything."