is there anyway to lock the grid.
 

I am trying to learn how to model by placing an image plane in the perspective view, that way I can line up my elements perfect. I usually start of with a ground plane, I make a new camera and move the grid down,but as I scale it up it seems like the grid moves back up.I know you can place elements using the background as a template.

You dont lock the grid to a position, you lock the cameras translates rotates etc select them in the channel editor right click over them and go to lock selected, when youve lined up the grid with something in the picture (to get a point of reference)

Also to get the correct perspective you migh have to adjust the cameras properties to match the camera that took the picture as i'm hazarding a guess that youll want to know why some things dont appear to line up correctly when you start to model them in the image. YOu can "fudge it" playing arround with the settings.

Have a look into camera projection as that should help you out

thanks gster.