I've never done just a tail, but the easiest way to get the bone out ot the hide is to take your knife and roll the tail down an inch or so the put the bone in a vise. take 2 screwdrivers and pinch the exposed bone and pull the tail off w/ the screwdrivers. Be very careful when you get down to the last inch or so because you don't want to tear the end of the tail. It will take some effort to get started but then it will zip right off. Like I said I've never done just the tail but when its on the carcass its pretty easy.
Then just rub some borax into the tail, and let it dry out it will get stiff so you don't need to fill it w/ anything. Cured enough for what you have planned. No need to have it tanned.