These two examples are taken from the recent military situation in Iraq, but can easily be translated into supervisory issues in police work. "Walking the line" can be quite a bit harder for police supervisors, because sergeants and lieutenants need to go out and find their officers at calls and traffic stops in order to interact with them.
But the principles are the same; the officers should be properly trained and equipped, they should be rested, fed, and watered as the situation allows; and they better be doing the morally and ethically right thing. The only way to know is for police leaders to be tireless in the day-to-day supervision of their officers, their squads, and their watches.
Supervision is not an intrusion, nor should it be perceived by officers to be interference in the performance of their duties. If that is the case, you have an officer that needs counseling or retraining. I have found that once the officers realize I care about the department, the unit, doing good police work, and them as individuals, this is rarely a problem.
Other than a few rare cases, officers who are righteous and feel that they are well supported never have a problem with supervisors visiting their calls. Unfortunately, many officers find supervisor visits are too rare an occurrence.
Following are some ways I have found to be excellent approaches to "walking the line" in police supervision. Rather than single out individual officers, I like to conduct mass inspections of personnel, equipment, and vehicles as it gives me an indication of who needs more attention. Backing up officers on calls and traffic stops gives me an indication as to whether or not officers are using good tactics and professionally dealing with the public.