In the context of Singapore, i think the best method to deal with the Astros is to pre-empt it.
Detection of Astros:
We can and i believe, we are already trying to shop or design a system for which we can monitor land activities of our neighbours at real time. In another words, we have to invest into high endurance system which can provide intelligence feedback, real time, all the time.
Although 'all the time' is a little impossible here where no system is technical-human blunder proof, however the phrase 'high endurance' would explain that interval between each real time feedback must be of minimal.
Systems of such available in the market is the Phalcon, JSTAR (not so available though) and perhaps the British Astro.
Such radar surveillence system could be mount on civilain modified aircraft, current military transport aircraft and UAV. If we are consistent in our research, we would know of the developement of the LALEE. Since they intent to design the LALEE as a High-Attitude Low-endurance (HALE) UAV able to carry a 3m by 9m radar ( if memory serve mi right ), i wont be surprise if the LALEE possess such capability (perhaps something similar to the Phalcon).
Such surveillence system will allow Singapore to monitor land activity. Perhaps with a ''lock-on'' feature, we are track our friend's Astros as much as technology allow us to do so. Any sign of bizarre movements will alert us to take precaution against such attack.
Employing such system is onli feasible to certain extent. The Astros could still rely on the aegis of the forest. In this case, we can depend on Human Intelligence. No war start over night. If tension raises, we can sent in special operation forces to perform armed/unarmed recon in Malaysia before the start of war. SOF troops will dig-in at as much clearings as possible in the radius 80km from Singapore.
As u know W.Malaysia is a peninsula, our focus now is very much reduced. In those dig-ins, SOF troops will be armed with anti-tank weapons ready to take out any Astros if they will to come out of their hideout and ready for fire. Although thus method is not fool-proof, i will say that it is still feasible. Understanding that Johor have very think jungles with little clearings and W.Malaysia is a peninsula, our focus is very very much reduced. Just monitor the Urban areas with our ''eyes in the sky'' cum some HUMINT personnels and monitor the jungle clearings with specially trained SOF.
To supplement the SOF, we can also employ small tactical UAVs armed with land-attack Missiles (perhaps Hellfire) and a small land-surveillence radar (Longbow is in my mind). This UAV with control signature will loiter in hotzones ready to feed HQ with ground situation and ready to attack any Astros unit upon the order. Such feedback is also useful for the HQ to compare feedbacks from our eye in the sky to ensure a minimal intelligence blunder.
Ways to get the Astros off the surface of the earth:
Specially trained (perhaps solely for Artillery hunting, lol) SOF elements in Malaysia could be a real threat because of the simple reason that...., they could be anywhere, anyone and may employ any method, determine to destroy the Astros.
Missile armed UAV loiter at any one time over hotspot will also be a nuisance to the Astros. Together with the eye in the sky, the UAV will loiter onli areas SOF can go and get clearer picture over the area. Armed with missile also enable them to wack the Astros in the cue of an order.
Stand off weapons employed by the RSAF in the future could be useful to take out Astros if they are in their storage ground. In the field and if time permits, smart anti-tank cluster munition launch miles away, dispersed over the Astros unit will create havoc. If Astros is already deployed for a war footing, i believe a real-time loitering device with a killing power is still the best weapon agaisnt those menacing beast.
Jus in case those menacing beast release their rockets, we can employ new laser weaponary agaisnt the incoming rockets. New missile systems such as improve Aster30 could be use to intercept incoming detectable rockets.
In case those rocket land on us...., lets pray hard that our research on strengthening vital locations is a success. Our opponent will surely employ penetrating weapons and now it is technology we employed that will have to prove such weapons wrong. Our maintenence and repair team have to be armed with the best technology and skill to swiftly restore any damage asserts. A diversion in weapons in Singapore have to be establish, i dun wanna see an easy kaput of 70 F-16s in Tengah over one night.....