At Denver's Elitch Gardens, a privately owned amusement park, off-duty city police patrol the grounds to protect patrons from rowdy customers. The security force is paid by the company to work part-time at the park -- a practice that the city of Denver encourages.

The eagerness of police to work extra hours provides many companies -- ranging from restaurants and clubs to banks, warehouses, and department stores -- with a readily available source of well-trained, part-time security labor. In Dallas, for example, a police department spokeswoman estimates that 80% of the city's force takes off-duty work. In Atlanta, where about 35% of the city police work part-time, officials have to approve each off-duty job. In Denver, the city has established an office of secondary employment to help local business-people hire a police officer.

Clearly, the benefit of using off-duty cops is the knowledge that your new employee has received at least basic training in police work. For instance, no officer on the Denver police force with less than one year's experience can accept an off-duty job. Private security firms often can't match that record. The costs of hiring a cop, however, are likely to be high. The Denver police department suggests that officers accept no less than $15 per hour for their services, compared with rates half that amount charged by some private security firms. But each officer is free to negotiate his or her own wage, and many will accept less in exchange for longer-term, stable employment.

Some cities do put limits on the type of work off-duty police are allowed to accept. Dallas police officers must wear their uniforms and can't work where alcoholic beverages are served. In Denver, police aren't allowed to take jobs that are considered a conflict of interest with police work. That means, for example, an off-duty detective can't investigate drug use in a company.

At 96-year-old Elitch Gardens, management has chosen to use both uniformed and plainclothes police, says Steven Mast, the company's financial officer. "All of us feel more comfortable with the use of real police officers," Mast notes. "It's effective with the public. And when there are problems, the police officers are trained in how to handle them. They already know the system.