Boy its really too bad you ask now, after the fact. Borax is not a preservative. At best its a modest bug proofer. Velvet is nothing more then living skin. If you soak it, etc, itll rot just like skins do. The best way to handle velvet antlers is to freeze immediately. From there you have options. Deer antlers in September velvet are a lot different than caribou in velvet, or deer antlers in velvet from earlier in the year. Taxidermists often know how to chase the blood from the velvet and even the antlers and replace it with a preservative. Sometimes if the velvet was ready to peel, you can leave them in the freezer until winter, then leave them out to dry on the cold dry weather of winter. Bugs wont get it then as fresh flesh, but they might later as dried tissue. Thats why we as professionals preserve or freeze dry them. Theres tons more about this, if anyone really needs more help, feel free to call me, Ill try to steer you right, with a taxidermist in your area. 585-637-2450.