I've always wanted something like license points for law enforcement officers. Every time they have a valid complaint/incident, the LEO looses a point of their national LEO "licence". Pair that with their dept. liability insurance bond, and once they drop below some threshold their insurance cost goes up or has to be self-funded. If it drops below another threshold they're uninsurable by any department and/or loose their national level credentials.

If this licensing entity is external to the force it would hopefully be more likely to remain unbiased, and this kind of national level of oversight would prevent bad apples from just moving to some other area to dodge a bad reputation/incident.