To prevent yourself or someone else from winding up unexpectedly splayed on the floor, you might need to secure a rug -- and there are two ways to do it. One is to lay carpet tape on the floor to hold the rug, but you'll need to redo the tape whenever you move the rug. The other way is to use underpadding. The rug can slip on the padding, however, and may require frequent adjustment. Combining these two solutions keeps the rug where it is while protecting the floor from sticky tape.
Turn the rug over, lay it on a flat surface, and clean off all the dirt with a vacuum.
Unroll enough rubber underpadding to cover the back of the rug and trim it with scissors so that it's a inch shorter on all sides than the edges of the rug. Remove it and set it aside.
Stick double-sided carpet tape on the back of the rug. Run strips of tape along the entire perimeter, laying the tape about an inch from the edges. Stick two or three strips in the middle.
Peel the backing from the tape and stick the underpadding to it. Center the underpadding on the rug and then press down on it to stick it to the tape.
Place the rug where you want it. It won't move.