A modest proposal for a new standard term in golden parachutes

Again this month we're exposed to disgusting scenes of CEOs and other senior executives getting big severance packages after steering their companies over the cliff and, in the case of Lehman Brothers, into bankruptcy. A typical senior executive contract provides that if the executive is fired for any reason other than commission of a felony all his benefits are immediately vested and he gets a multi-million dollar payment or series of payments. Would it be asking too much of boards of directors to insist that these contracts provide they can also fire a CEO, COO or CFO without any vesting or severance payments if the stock price declines below 50% of what it was when the agreement was signed? Other than the likely lack of spine, what's the argument against that?