rakeless riders generally need to master a technique called the "skip stop." This is a way that you can actually lock up the rear wheel using your legs alone.

• If you lock one leg at the bottom of the pedal stroke, as the pedal rises it will start to lift your body upward.
• When the cranks get horizontal, pull up on the front pedal, while pushing down on the rear one.
• Because your body will have acquired upward momentum, when you yank up with the front foot this will temporarily partially unweight the rear wheel, making it possible to initiate a skid.

Since sliding friction is less than sticking friction, once the tire starts to skid, you will generally be able to maintain the skid until you've stopped or at least slowed down as much as you want to.
You have to really want to do it, you can't be tentative! It's easier when you're going faster.
The lower your gear , the more effectively you can "brake" by resisting with your legs. Despite what some folks will tell you, you can not stop nearly as short this way as you can by using a good front brake.