the only way to prevent it blowing is to buy a new one from toyota and ask them to torque it down properly lol
sorry but it will blow eventually
what i would do is save up the $$ for the new hg and bolts and get the head checked for warpage etc... clean surfaces new toyota hg and new toyota bolts torqued to 72ft lbs (or arp head studs torqued to 82ft lbs with arp moly lube) and do it before it blows... or when you see the very first symptoms...
temp spiking
overheating in traffic
overheating on boost
is just some symptoms
of course if you have these problems try the simple things first... radiator flush, water pump, radiator cap, thermostat
if it's from a dealer see if you can score some sort of warranty that covers the hg
