Check out a product from the Flood Company called UV-CWF. This stuff is good and last a good year or two. Remember, these stains do not last forever and have to be periodically re done.
Since your fence is so old, it will soak up the stuff like you would not believe.
Try a product by Sherwin Williams that I have used many times on cedar shake siding. Its called Woodscapes, it can be mixed to any color and is a stain / paint. Much cheaper than the Flood product.