Both dirt and threats work well only if they're accompanied by payment and perks. If it were only the dirt or only the threats, they'd have people backed into a corner where they'd have nothing to lose, and people with nothing to lose are loose cannons who are hard to control (outside a bullet to the head, which is usually the last resort). Threaten them, yes, of course, that's a given ... but pay them well, too. Make them complicit. Keep them inside the tent pissing out instead of exiling them outside pissing in. That's how the mob gets their soldiers' hearts and souls as well, instead of just their fear.