Use the hair from farther up towards the tip of the tail. The hair at the bottom of bucktails is often more like body hair in texture and behavior when tying. The hair normally get progressively harder, finer, and less likely to flair and spin as you move towards the tip of the tail.
Alternately, sometimes the flaring can be controlled by simply tying the hair in closer to the tips of the hairs, but this limits the length of the wings. I can't imagine you are tying mickey finns that require the entire length of the hair to be used, but I could be wrong.
Finally, I think the issue of hair length and texture is a great reason to be very selective when buying materials. If there are say, ten bucktails on the rack when I go into a fly shop, I look at all ten and only buy the one(s) with the best characteristics for their intended use. In the case of bucktail, I usually want a tail that has long, straight, fine hair that does not have a very thick, spongy base like body hair.
