It's a foreclosure that you don't fight. You just offer the deed to the lender so they don't go through the full foreclosure filing. The impact on your credit is the same, but it starts the clock ticking to recovery sooner.
If you are not finding a buyer start dropping the price regularly. If you owe more than it's worth, do a short sale. Short sales are generally less damaging to your credit and you can continue to live in the house while it's on the market.