Fobus makes a decent paddle holster. If you screw the tension screw down all they way the retention isn't bad. However it's not the tightest against the body but it does conceal pretty well under a jacket or something.
Wild Bill's Concealment makes a solid paddle holster, and I see they have one available for the Shield. I have one for my P226, and it hugs against my body more so than any other paddle holster I have used, and it does a good job at retaining the pistol, even though there are no retention adjustments.