Just don't let them in?
I never answer the door to anybody who I don't know, lets be honest if somebody random comes to your door how often is it for something that will benefit you? They are either salesmen, Jehovahs witnesses or pikey neighbours wanting to borrow something. We never had a TV license in our old house, they probably sent the TV license inspectors round various times but we never let them in, if we were all in the sitting room watching the TV we could never hear the door anyway, that would be ironic haha.