Employers can only engage in such snoopy behaviors because employees allow them to do so. The first time an employee is dismissed for off-work behavior, every employee who doesn't want to be the next victim should submit his or her two-weeks' notice. Big Brother can't exist without little brothers and little sisters to push around.

If an employer is a big enough asshole to monitor your off-work behavior, screw him. Go to work for someone else. Better yet, become self-employed. You can't be fired when you work for yourself.