How did the edmontosaurus defend itself?

Like most herbivores, Apatosaurus didn't have a lot of means of fighting back against predators. Thanks to footprints, we know that young Apatosaurus could run away from predators on two legs like a basilisk. Once they got larger, though, that was no longer possible. At that point, their large size made them too large for most predators, except for Allosaurus. They could have used their tail like a whip in an attempt to ward off Allosaurus, but how effective that was I am not sure.