It IS impossible to train for every possible way you can be attacked, because just when you think you've covered every possibility -- someone'll disguise a lead pipe with a feather duster, and you haven't practiced against feather dusters. But it's not impossible to train against likely attacks and likely methods. Do some research into how attacks tend to happen, the most likely weapons to encounter, and so on. Also, truthfully, their just ain't but so many ways to move the human body around. Especially with a purpose of causing harm to someone else. It's also possible to train in enough possibilities that you'll find a workable response to any attack -- even the feather duster.