The key is to be polite but assertive. If you yell from behind your door "Hell no PIG! You're never coming inside and it is my RIGHT to say no!!" then it may arouse suspicion. If instead you say " I'm sorry, I wasn't expecting company and my place is a mess. Lets talk outside instead." they will likely not think twice about it. If you treat a cop like the human they are they will probably be more trusting. Funny how that works...
That's exactly right. When the above piece of advice was told to me, the suggested phrasing was something like "If you don't mind, I'd rather discuss this out here with you," and as you say this, pull the door closed behind you.