One incentive worth considering is a take-home car. An officer considering an agency that doesn't offer this may think twice when considering the cost of another private vehicle, increased gas and insurance, etc. Take-home cars increase public visibility of police and decrease response times to major emergencies and officers needing help. They are very common in some areas, such as Florida, and rare in other regions, such as the west coast.
A similar benefit is housing. A western hospital provides temporary housing to new employees, and the Mountain View (CA) Police Department has dorm-like housing where employees can stay while off duty after their 12 hour shifts. They then go home on their 3-4 days off a week. Some departments allow personnel to park their travel trailers in the parking lot. The 10- or 12 hour day work schedule allow the employee to live in more affordable or rural areas with good schools. It also saves briefing time, gas, and has other benefits.
Old rules die hard, but many agencies have a "once you're gone, you're gone" policy. Consider changing the rules to allow an employee to return within a year without having to start from scratch.
When senior officers with specialized knowledge are planning to leave, it is important for the department to recognize that and take steps for junior officers to work with them to gain some of that information. In my former agency, Sgt. Bob Rice handled all the special events, traffic control, related PR, and motor assignments. His retirement was a big loss to the agency. With him went a great deal of institutional knowledge. Make sure that gets passed down.
A final issue for those trying to understand retention is to understand the difference in generations. Baby boomers are different than so called Generation X and Y officers. There are articles and training on this, and an understanding the distinctions will prove most helpful.
In summary, some personnel losses may be unavoidable and even beneficial. On the other hand, improved retention begins at the recruiting phase, to be sure the applicant understands what they are getting into. Family must be included, all along the way. This may include some consideration of child care needs. Consider a mentoring system. Changes in morale, working conditions, job security, housing and scheduling are factors that can affect retention. Take-home patrol cars can also be a nice draw.
Retirees may be retained in various ways, so as to soften the loss from their departure. Try to understand the different expectations and needs associated with baby boomers, and Generations X & Y.
Retaining good officers saves the department valuable re-training costs and should not be ignored.