"The favourable results of missile defence systems are obtained by putting homing beacons in the incoming target missile, and in spite of this sometimes miss." - Clickfool This is not totally true. As early as 1960 the US was able to intercept an incoming Honest John with a Nike Hercules, or an incoming Corporal with a Nike Zeus. We can now intercept an incoming SCUD with a Patriot PAC III (or II for that matter). There are limits to the technology, and it cannot defeat a technically savvy foe, but limited missile defense is possible.
Australia to spend $64.9 billion on ships, submarines over 20 years (Reuters)
from the article: Intercepting Qassam rockets