You may not have noticed (and that's the point), but if you flip your seat cushion over, you will see tiny rubber-like bumps. Those bumps actually help the seat stay in place & as an added protection, there are 2 lateral straps on each side of the Bike Seat Cushion.
Fasten those straps by knotting them together under your bike saddle. Tighten the drawstring (located in the back of the bike seat cushion) & your seat cushion is guaranteed not to move around - even in super intense situations.