Do a internet search on skinning, preserving, stretching, tanning, etc.... Skin them the way you want them and then be sure to get the flesh and fat off of them. If you are going to tan them, than you can start the process then, or salt dry them to preserve. You can (once fleshed) stretch and dry them without salt and often they will last some time. Borax will also help to dry them out more quickly if you don't salt. The smell may be the flesh, fat, blood, etc. You want them clean. A good soak in cold water will take out most blood. Some wash with dawn to help with fat, others hand wash with water and a bit of laundry detergent. Use cold water. There are countless ways you can tan them and many different things you can do with them to display.