I firmly believe that no matter what you do, if the wind is blowing from you to the deer, it will smell you. You may get lucky and the breeze blow over their heads, but that is just what it is. Luck. Now I do use scent free detergents, soap and shampoo and I do put my clothes, boots and backpack out under my covered front porch for a couple of days prior to hunting. That is just to keep my scent down but I know it will not eliminate it. 12' is not very high and is probably your main problem other than the wind direction. I hunt out of 15' stands myself as that is as high as I wish to go, but have been very fortunate in that I have not been busted but a couple of times. All my buddies go up to at least 20' which is way better for scent control. I also pay close attention to the wind direction before deciding on which stand to use. That also helps alot.
Are you sure they are smelling you and not just seeing movement or that you are sky lined for lack of cover? That could also be a problem at that height. Best of luck to you!