Whitetail Institute offers several supplements that are exceptional. The deer will literally paw at and eat the dirt to get this stuff:

http://www.whitetailinstitute.com/products/3006/

http://www.whitetailinstitute.com/products/edge/



The picture here shows a bachelor group of a supplemental feeding area. Also, if you look closely around the stump you can see where it has been dug out by deer trying to get the minerals.