Maintenance of the wood.
Firstly you must realize that wood needs to be maintained if it is to last throughout its life expectancy. As a rule, wooden panels and posts should be painted on an annual basis with paints or sealants sold at places such as Wickes DIY store. Wooden panels are usually pressure treated to aid in its life expectancy; this is usually around 10 to 15 years.
Replacement of the fence.
After about 15 years you should start to prepare yourself for replacement of the posts. This will become increasingly frequent until the day that you should look at digging the fence up and constructing a new one. About 20 years is the time when you should expect to have to replace your fence completely. Some of the woods available for your fence include Whitewood Stockade, Eastern cedar, Oak, Western cedar and Sweet Chestnut.
A couple of weather resistant woods.
Sweet Chestnut is one of the most popular choices. Introduced by the Romans, this wood has naturalized to become a very durable and suitable wood for fencing.
Cedar is particularly resistant to things such as fungi and insects as it consists of naturally occurring oils in its timber. This wood is also of low-density which means that it is less likely to warp over time.
The main reasons behind a dying fence.
Like the old saying goes, "You get what you pay for", this is also true when buying the right wood. The higher the price usually means the better and more resistant wood you are buying. Pressure treated wood is designed to be resistant to termites and decay but be aware that some woods do not come treated with a sealer and some do; the latter being the more expensive of the two.
Sealant is an important factor when choosing your wood. If it has not been sealed, do it immediately to avoid warps and seepages in the future, especially in the more exposed areas of your wooden fence.