I don't know if any LE agency that uses a 'polygraph' to 'weed out' potential hires. Most LE agencies today use a 'VSA', or 'Voice Stress Analyzer' for such tasks.
General questions inquire about 'previous arrests, drug use, etc'. The VSA is extremely sensitive. There's a reason why polygraphs are no longer admissible in court.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .