Nowhere am I advocating that. I'm only suggesting "Am I free to leave?" and silence in response to anything but an unequivocal "Yes" to the question. And noting their leaving is also an implicit Yes.

Now, depending on your reading of the situation and the cop(s), you could play games with an equivocal answer, i.e. follow with "OK, you are detaining me", and if they object, go back to the free to leave theme, then press them on deciding one or the other. But that's not what I think one should generally do.