Wrap a piece of rubbery material, such as non-slip cabinet liner around your bench pin. The rubbery material is wrapped around the bench pin with an elastic, to prevent slipping while using your flex-shaft. This method helps with materials, such as wax, wood, and stone. The non-skid cabinet material can also be used as a cushion to prevent scratch marks and dents while sanding, finishing, and refining your pieces. (This material has a foamy texture lending bounce and cushion.) Here are the materials needed for non-slipping/cushioning:
The rubbery/foamy material is wrapped around the bench pin with an elastic, to create non-slipping while using your flex-shaft. This method helps with materials such as wax, wood, and stone.
Wrapping a piece of fabric around your bench-pin also assists with cushioning objects. A cotton material I find works best for the sanding, finishing, and refining phases. The fabric does not hold a bounce and works best for final phases of finishing. The material can be attached with an elastic, the same way the cabinet liner is attached.
Another tip: While handling slippery objects and using your flex-shaft, wear a non-slip glove (I find a garden glove works best. But any glove with grip, human-made or a leather material works well.) This helps with handling and grip.
Link for cabinet liner, found on eBay:
http://www.ebay.com/bhp/non-slip-drawer-liner
Gloves found at any home appliance/hardware shop.