It is not necessarily the event that is interfering with public access that you allude to but rather the protest of said event.
Take the recent CPAC Conference in the nations capitol. It was the
protesters that interfered with both the peaceful public and attendees (Mr. Breitbart not withstanding) access to and from the conference.
Along a similar thread, there is a report of the Mayor of Tampa which hosting one of the political conventions this year trying to have concealed carry revoked during the week of - in areas controlled by the city, yet outside of the National Security Zone. He is being stymied by Florida law - here's the story.
Tampa may seek Gov. Rick Scott's help keeping guns away from RNC protests