How to Prevent Small Town Property Manager From Disclosing Info

[William Coet]

Is there anything that can be done to prevent a property manager from disclosing info, especially financial info?  This could particularly be a problem in small town markets.  This question is directed more towards hiring someone in a small town where professional managers aren't available.  I'm considering investing in an area like this.
Can a non-disclosure-agreement work?
Are there ways to judge a person's character/background to determine they won't spread information?  I understand that rental rates are available to anyone who asks, but that doesn't mean a property manager should be hanging out at the local bar telling everyone how much income there is (especially when they don't always know all of the expenses).

Thanks!