A fast easy way to get more weight on your side is to just politely declare, "No offense, officer, I know you are just doing your job; but I do not consent to an ecounter with you." If this is the first thing an OCer says, it immediately establishes the nature of the encounter as non-consensual.
I got that idea from a VA court case. That appellate court wrote to the effect that 4th Amendment (search and seizure) case law recognized three types of police-citizen encounters: 1) consensual encounters, 2) brief minimally intrusive investigatory detentions based on articulable facts (Terry Stops), and 3) highly intrusive custodial arrests. I just applied logic that already existed. It is already understood that a person can refuse consent to a search or seizure during an encounter. It is no leap at all to apply consent to the encounter itself. If you refuse consent to the encounter at the very beginning, it cannot possibly be a consensual encounter from that moment forward.
If you think about it a little bit, it is obvious why the courts have to resort to figuring out whether a Terry Stop seizure of the person occurred by looking at how many cops, whether there was a show of authority, physical touching, tone of the cop's voice, words the cop actually said or didn't say, whether a reasonable person would feel free to leave, etc., etc., etc. The courts are using all these indirect indicators simply because the citizen did not make directly clear his consent or refusal himself.
So, the simplest thing one can do is to make these words the first thing he says, [politely], "No offense...but, I do not consent to an encounter with you, officer."
If you refuse consent to the encounter itself at the very beginning, it cannot possibly be a consensual encounter from that moment forward. This immediately throws the onus on the cop to have genuine RAS for a Terry Stop if he wants to continue the encounter. If the cop continues the encounter for even one more question or comment, just reinforce the refused consent to the encounter. For example, "I wish to be released and be on my way right this instant, officer."* And, just keep sprinkling that refusal among your other rights-exercising comments like "I wouldn't answer any questions without my attorney", or "I don't consent to any searches." Asking, "Am I free to go?" at various points along the way also helps establish that you want to leave; but its not as strong and clear.
Refusing consent to the encounter itself also undercuts and negates all the cute conversational tricks cops play on this point. For example, some OCers have asked if they were being detained and were told no. When they immediately then asked if they were free to leave they were also told no, revealing that the earlier no was designed to confuse or deceive the detainee into either talking or attempting to leave so the cop could physically grab him. If you refuse consent to the encounter, you take all that initiative out of the cop's hands.
Of course, if one wants to first find out why the cop is approaching him, the OCer can always wait a moment to hear what the cop has to say before refusing consent to the encounter. Maybe the cop is going to ask whether the OCer saw a certain child who is missing. We've never had such a reported encounter, but lets say. As soon as the OCer recognizes he is being investigated, he can refuse consent, "Oh, I see, officer. Well, sorry. I know you're just doing your job but I no longer consent to an encounter with you." In Miranda vs Arizona, the arrestee can stop answering custodial interrogation questions at any time. There is no reason an OCer's initial consent to an encounter cannot be revoked at any time.
Its important for new readers to understand that we're talking about a verbal refusal. Not a physical refusal. We're talking about consent (willingness), not enforcing that unwillingness by physical action.
Separately, I would repeatedly ask, "Am I free to leave?" But not to establish refused consent. I would ask it because I'm not giving the cops any excuses to physically grab me, throw me on the ground, and cuff me. I ain't budging until I have express permission to leave. I have read too many reports of cops playing word games during encounters and lying in pretrial hearings to risk giving them an excuse to manhandle me or arrest me for (obstruction?) if I try to leave. I'm going to assume I am seized if the cop continues the encounter for even one comment or question beyond my refused consent to the encounter.
*You never know, the cop might just hand you a Title 42 violation of rights. We recently had a report of a cop saying, "You'll be on your way as soon as you answer some questions." Yeehaw!!! Coercion to waive the Fifth Amendment right against self-incrimation/right to remain silent!! That will look real good in a formal written complaint or lawsuit, especially if you recorded the encounter.