An improvement would be to be able to provide a strap or tie-down that could be used at the middle of the blind too or in other places along the length of the tie-down rod.  This works perfect if you have a blind of the proper length to fit your railings or porch posts.  If you do not the ends hang in space. 

An alternative I suppose would be to supply small bags to be filled with sand provided by the user and extended with a line to the existing tie down points to the porch or ground level.  Just a thought.