I don't know a thing about protection, beyond what little I've been able to see (from linked videos) and read from those of you who understand it.  So please make allowances for my naive questions...  Why do the dogs only seize the padded arm?  Were a real-life intruder to wear such an apparatus, would a trained dog "go" for that, as opposed to some other, softer and more vulnerable areas?    }:-O