Ok, I think what you're really asking is "how can I benefit from a collapse in the price of gold?" :-)
And that's easy. (The hard part's making that kind of call with money on the line...)
GLD is entirely physical gold sitting in a bank vault. In New York, I believe. You could simply sell it short.
Alternatively, you could buy a put option on it. Even more risky, you could sell a (naked) call option on it. i.e. you receive the option premium up front, and if it expires worthless you keep the money. Of course, if gold goes up, you're on the hook. (Don't do this.)
(the "Don't do this" was added by Chris W. Rea. I agree that selling naked options is best avoided, but I'm not going to tell you what to do. What I should have done was make clear that your potential losses are unlimited when selling naked calls. For example, if you sold a single GLD naked call, and gold went to shoot to $1,000,000/oz, you'd be on the hook for around $10,000,000. An unrealistic example, perhaps, but one that's worth pondering to grasp the risk you'd be exposing yourself to with selling naked calls. -- Patches)
Alternative ETFs that work the same, holding physical gold, are
SGOL. With those the gold is stored in London and Switzerland, respectively, if I remember right.
Gold peaked around $1900 and is now back down to the $1500s. So, is the run over, and it's all downhill from here? Or is it a simple retracement, gathering strength to push past $2000? I have no idea.
And I make no recommendations.