That is what I was thinking it all depends on what cop shows up.
Not once the threat was made, as long as weren't brandishing the gun first (and you had it legally stowed in your vehicle, whatever your local laws on that are...and that might be more a depends on which cop shows up thing how technical he'll get with that).
As a general rule, you can always park your vehicle, lock any gates behind you on the way in, etc. and if that just happens to block in another vehicle on private property, that's just unfortunate. You're not trying to stop them from leaving in the vehicle, it just happens the vehicle is blocked in. You can wait for a cop to come and ask you to let them out
But unless you want to go into the thin ice of trying to make a bonafide "citizens arrest" just remember that the people can always just walk away. If they haven't threatened you and you don't let them leave, then you risk it being called kidnapping. Now the dirt bags are usually too dumb to realize they're free to secure their property by locking the doors and walking away...
