Joe, a year ago I personally gave information on state preemption and municipal code violations to the police training officer (coordinator) and to the city attorney. The expectation was to get the proper information to the cop on the beat and to correct the municipal codes. We were basically ignored. The cop on the street was given misinformation leading to Bennie's confrontations.
At the same time I told them that it fell onto our shoulders to inform the public about their rights so that people do not to freak out and call the police if they (the people) are in a situation or place where someone is open carrying.
And so it continues.
fetch it is good you were or are looking into correcting this but you approached people that cannot or do not change City Ordinances to get this accomplished.
The Mayor and City Council are the ones that need to be addressed on the issues of ordinances, as they have the power to change or remove the city ordinances and thus the Police claim to follow them will no longer be able to rely upon it.
Granted there are City or County Councils will resist this and others will be happy to comply, but that is where the battle needs to be taken.
Since you are having a Picnic to protest this you need and others need to get in contact with the Mayor and City Council (all of them if possible) ie CALL ON THE PHONE OR MEET IN PERSON and discuss this issue ahead of time.
If you get shinned on then you need to attend the next City Council Meeting and sign up during the Public Comment Portion and lay it out for them, bring copies for all members and the secretary so it becomes Public Record.
After this is done then you have the News Media and Events as you are talking about to fall back upon.
By going this route you will likely bring supporters from the Mayor or City Council instead of appearing to them as you are attacking them when in essence they may or may not know of the problem.
My experience in changing these gun bans in Yakima City and County was welcomed and statements of appreciation on the information and help to provide an easy resolution.