What has done wonders for Lacey's tail is just keeping it braided and Cowboy Magic detangler-ed. I had previously used Show Sheen on it quite extensively and while that worked to keep it tangle free, it kinda made her tail tough and brittle feeling (her tail normally feels and looks like human hair in the weirdest way possible).
And then, over the winter I wanted to get her tail even and pretty so I started braiding it and using enough cowboy magic that the inside of the braid still smells like it when I take the braid out (once every two weeks or so). I also washed it about once a month. And now, her tail is AMAZING. It is SO soft, it doesn't tangle when I let it out of the braid to work her for a few hours, and it's very shiny (for a white tail).
I'm really excited for the summer when I can show it off. Heeheehee