Get the footer to be at the bottom. Unless there's a sidebar where it should be at the bottom only if width > 1500px, else have it flow naturally under the collapsed sidebar unless that's too short. For some cases, have it below the viewport instead of at the bottom. For others, expand a subcontainer instead of the main container to lay out something else correctly. For yet others, make it's to be a specific pixel offset from the viewport bottom. And all must account for height of footer, page container, sidebar, page contents, and specific requirements.