There is a gate, with a warning. That stops most of the delivery drivers. Tourists, not so much.
Maybe add a sign with an admission cost and warning that rescues cost a minimum $1000?
Tell them you have two options, you call the police or they pay the posted fees and you pull them out.
Being the nice guy for the first one or two idiots is fine, but I imagine your inconvenience has a cost?
No amount of complaining will remove it. It only exists on Google maps, not on Apple Maps, Waze, Openstreet, or the various garmin/navitronics outdoor/boating navigation apps I have.