Cut the front and rear hooves off a deer four or five inches above ankle joint, low enough on the leg that under the skin is very little meat and mostly just the tendons and other connective tissue. You can use a power saw, but a sharp hand saw is almost as easy.
Use a piece of lath cut to the length of the hoof as a splint to hold the hoof in a straight position if you plan to make something from it with the hoof/ankle/leg in that position. Straighten the hoof and lash the lath in place with a length of twine.
Anchor the hoof/ankle/leg in a 90-degree bend at the ankle for making a gun rack or coat rack by connecting the hoof and leg bone with a piece of twine.
Mix 2 cups of borax in a gallon of water in a plastic bucket.
Submerge the hooves in the borax solution for 24 hours. The borax is a preservative that will guard the perishable parts of the hoof from decay until they can be dried and permanently preserved.
Remove the hooves from the borax solution, dry as thoroughly as possible with paper towels, then hang them in a well-vented area where the hair and hooves can air-dry completely.
Place the hooves in a paper sack and loosely secure the sack closed. The sack isn’t strictly necessary, but if you plan to put the hooves in a household freezer, most other family members will prefer they are in a sack, rather than laying loose against the edible foods inside.
Place the sack in a freezer, preferably a frost-free model such as in most refrigerator/freezer combinations. Frost-free freezers subject contents to freezer burn much more rapidly than non-frost-free models.
Leave the hooves in a frost-free freezer for at least six months or in a non-frost-free machine for a full year. You can leave them in either freezer indefinitely longer.
Wait until the weather report indicates four or more days of warm, sunny weather, then remove the hooves from the freezer and place them in a warm, sunny location so they soak up the sun during the bulk of each sunny day.
Turn the hooves over each day so each side receives equal amounts of sun.
Remove the splints or ties that are keeping the hooves positioned as you want them. They will be as stiff as a board by now and ready for whatever use you have planned for them next.