If there is no sign telling patrons an area is off limits, you'll have to inform verbally.
As soon as she tells someone, including a LEO, that they cannot be behind the bar AND to get out from behind the bar, they have been advised they are trespassing.
THE PROBLEM IS, as a misdemeanor, the LEO needs to see the infraction for themselves. How do you prosecute when the violator is a LEO? Get video and audio evidence to Internal Affairs as part of an official complaint.
THE PROBLEM IS, what kind of troubles will you get from the LEO's friends in that agency after you do something like that? You'll get a 60-minute response times to the next few bar fights, most likely.
The complaint needs to come from a third party.
Of course, that sounds like an invitation to hang out in a bar for long periods of time...