Boiled linseed oil if you are looking for "organic".

Al

It might be cheaper to use a water sealant,
the type of product you would put on a wood deck.

(Don't know what's in water sealant, sorry)

I'll second the vote for boiled linseed oil. It's from a renewable source, easy to use, and the $ compares favorably with harsher sealants. Not positive, but I think I read you can also add tints to color it.

Third the vote for linseed oil. Hope you can find it in gallons where you buy lumber. You can pour it around posts to help preserve wood below the ground. I believe during WWI and WWII that it was the primary oil used to finish and preserve gun stocks. Check your dictionary under "linseed" to confirm that it is environmentally friendly.

If you are painting the fence, there are a couple of new waterproofers that may be easier to apply. Just check what you are going to buy, because some of the commercial deck sealers have to be reapplied every couple of years.

Just remember that unless the neighbour's on the other side of the fence are doing the same thing, it won't help much. Also any oil finish you use will not be permanent.
Cheers,
Dee.