Eight, with all due respect, you are trivializing and generalizing beyond extreme in this case. If a trader has a crap strategy and poor risk controls, it wouldn't matter if it was a correlation or a technical study that spelled his demise.
I've had profitable correlations last for three weeks, and I've had profitable correlations last for seven years (and counting). The fact of the matter is that a statistically significant correlation with a fundamental driver is the most consistent edge in the business, in my opinion. When a correlation falls off below 90%, I stop using it. You test them routinely, and observe and trade them side-by-side in the live market.