On public property, maybe, on my property, no. If he feels uncomfortable with me having a possession of a weapon while I am on my property he is welcome to leave, unless he has a warrant for my arrest.
Well if he is performing his duties (responding to a call, chasing a guy, investigating something suspicious, whatever), he can do all kinds of stuff on your property - trespass, for example. And while he’s trespassing, he can certainly tell you to put your gun down.
Again, my legal degree came out of a Cracker Jack box...but a cop does not even need a warrant to cuff you and detain you on the scene, if he is trying to sort out a situation.
Not saying its right or wrong, but that’s the way it is.