Nate, no they are really not preventable, but keeping the heat low will help. You can quite often tell if a cap is going bad by some sonic indications, but it is possible that a cap won't fail first. It may be a resistor, or output transistor or anything. Since you don't really know what item will be first to fail, for sure, you can't do too much to prevent it, other than good general care, and using the amp within its design parameters(not pushing overly low impedances especially). After that, it's just the luck of the draw.