Roving patrols or check points?
I favor patrols. Roving patrols will actually catch those driving eratically because they require indicia such as swerving or driving 25 mph under the speed limit. Check points tend to catch people who are merely above the BAC level and not showing indicia.
The problem is that check points are far more easliy quanitfiable than having officers patrol and they "show the flag." If police do them they may be less effective, but they demonstrate that the police are doing thier job. And there comes a time to justify the budget . . .