Border Security? Sg have?

Astronotus Oscellatus: "Ever see two men on a motor bike...got pail, got wooden poles, got manual tile cutter, got tool bag...all loaded up and going to work...cannot be local...and many minivans overflowing with tools..."

YJ Tan: "Saw a JB-plate wagon in the HDB carpark loaded with tools and fittings for electrical works. Guy goes around getting work from contractors and he never pays for season parking, he just press the help button and lies to get the operator to lift the gate."

A foreigner/m'sian drives into Sg to do biz like plumbing, aircon, how does he gets tax for his earnings in Sg? Never?  Locals can be tracked, foreigners look for who? I say again, what kind of border security do we have, the level of tracking, the speed.  Sg is so open, simple plan, terror attack, come in as contractor, sub-con for govt project by main con, plan a sabotage.  Heck even an ordinary HDB renovation can be sabotage! Byeeee.

There are several issues here,
1. the ease of access to sg homes, infrastructures here,
2. the inability to enforce control, IRAS can't tax those freelancers who comes in and do biz, odd jobs.
3. besides police manpower shortage, better to solve potential loop holes. MHA better not sleep on this one.
4. the issue is not how much they earn, its they are undercutting local biz, some doing shoddy work, worst even contravene building regulations. what if they drill into a beam, stuck the drainage, shortcircuit the lifts????
5. the tenants loses for paying unregulated craftsman, HDB loses for structural damage (but hey who's complaining, end of lease they can just tear down and rebuild again, such minor setbacks does not interfere with GDP as long as damage is minor)
6. btw acccident between Sg vehicles and M'sian vehicles, Sg vehicles can't claim from M'sian vehicles insurance, pay so much COE kam lan?