I am not advocating walking away, but with the proper structure in place, you have options. Without the structure, you are at risk. If you have one property upside down and vacant and another with equity and rented, you can negotiate a payment plan with the lender if it is foreclosed, and when the other property goes up in value use the additional equity to repay the other note. But if you lose both properties, you will be out of luck.

I frequently set up an LLC for each property (or group of properties) and have those LLC's owned by a "master" LLC. Some clients also want to have the master LLC owned by a trust.