wavy larch panels are not very prone to rot, except where in contact with the ground or in a damp corner.
Fencing panels are unique in that they are either too wet (during rain) or too dry (at all other times) for the ideal level of moisture which woodrot requires. They are thin, and exposed to drying fresh air and wind. The thicker top-rails and bottom-rails rot first.
I use fence stains, and they do repel water when newish, because they leave a waxy tinted film. Use the biggest brush you can handle. Spraying, I hear, tends to drift over your garden, car, house, washing, overalls, dog, skin (and the neighbours).
A top brand like Cuprinol is supposed to keep its colour longer. I usually buy the cheapest own-brand in the biggest tubs. If you have lots of fence and want to delay the effort of recoating, the better one may save you work. The cost difference can be significant. All the water-based waxy stains are easy to recoat once weathered
Wilko have a half-price offer on some Cuprinol stain this week (various colours)
http://www.wilko.com/all-exterior-paint/cuprinol-less-mess-shed-fence-rustic-brown-5l/invt/0338574
their own brand is usually much cheaper
http://www.wilko.com/all-exterior-paint/wilko-timbercare-country-brown-5l/invt/0074038
Ducksback is more than twice the price.
http://www.wilko.com/all-exterior-p...or-shed-and-fences-forest-oak-5l/invt/0241775
B&Q mostly cheap. Their own-brand is watery.
http://www.diy.com/search?Ntt=fence+stain&Ns=p_price|0
For the garden gate, and soaking fence posts, I use a real timber preserver such as
http://www.wickes.co.uk/Wickes-High-Performance-Wood-Preserver-5L-Woodland-Green/p/170778
which contains insecticides and fungicides. it is spirit-based and much more expensive. Too good for a fence.