Many Las Vegans have been hit hard by foreclosures and underwater mortgages.  They might walk away from their home or take on debt when they sell an underpriced home.  But when an Air Force member does so, that servicemember risks losing security clearance - and in some cases, even lose their jobs.  The housing market has forced some servicemembers to live in trailers, or even move to different states.  How has the hard-hit market affected those at Nellis Air Force Base, and what options do they have left?  And how is their situation different than the average underwater homeowner?