I read a (just okay) near-future cyber dystopia novel called "Little Brother" once. It had this interesting segment where gait recognition was being used to track people instead of facial recognition because it was more reliable (I'm not sure whether this is true in reality, but regardless).

Anyway. The main character had an easy way of breaking it: toss some gravel in one of your shoes. It'll disrupt your natural walking pattern in a randomized way without you having to even think about it.