Exactly right Steve! Private property is just that; the owner makes the rules, as it should be. Otherwise, know your rights and assert them politely, but as firmly as the situation warrants.
I've had far more trouble from overzealous ninnies among the general public than from the police. The public generally believes they have a right to deny themselves, their kids, or their property being photographed IN public view (they don't); while you have a fair chance that the police actually know the law.