Rugs creep across carpet because the pile of the carpet lies in the opposite direction from the rug's pile. So, the pile moves and causes the rug on top to move too whenever someone walks on the carpet.

Do not use large piece of furniture to anchor the rug as it can pull the rug out of shape over time. Actually, its better to use a synthetic fleecy material to fit the back of the rug, which can stop the rug creep on carpets or hard floors.