Some walls are so bad that the best fix is to tear them out and install new drywall. Wall liner is the next-best fix. It's basically extra-thick, paintable wallpaper that acts as a big patch over the whole wall. Some versions are smooth; some have a textured or patterned surface. Fill cracks and holes with joint compound, prime the patches and then hang the liner just like wallpaper. A 55-sq.-ft. roll of wall liner costs about $16 at home centers, paint stores and online.