Police cannot "detain" you WITHOUT YOUR CONSENT. By continuing to stay there and by talking to them, you are giving your implied consent. But you may not leave if they are in the process of arresting you, since in that instance you would be "avoiding arrest."

What I have found useful when being detained is to say: "Am I under arrest? If not, then I would like to leave. And if I am under arrest, then I would like a lawyer." This alerts the cop that you know your constitutional rights and places the cop in jeopardy . . . either (i) s/he allows you to walk away or (ii) s/he must (A) determine that s/he has "probable cause" to arrest you, (B) arrest you and provide you with all requisite rights, and (C) refrain from asking you any further questions because you have asked for a lawyer.