When it comes to using certain power tools, like a belt sander or a router, it's crucial that the work piece is held firmly in position.
Sometimes, clamps that would hold a work piece secure simply get in the way of the tools.
A solution that is both practical and inexpensive is a roll of nonslip shelf liner. After cutting an appropriately sized piece of shelf liner off the roll, simply place it on your work bench. Place your workpiece on top of the shelf liner.
The wood you are sanding will now stay firmly in place.