Timber fences. All wooden parts should have been treated with wood preservative before the fence was erected. Panels and fencing posts are usually treated under pressure by the manufacturer. If you are buying timber to make your own fencing, probably the best preservative is still creosote, but this is highly toxic to plants when fresh. Other spirit-based preservatives are very effective, and treated wood can be used near plants only a short while after application, but are a lot more expensive.
If possible hardwood (oak, elm, etc.) should be used for all solid parts but this is very pricey and not always easy to come by. Creosote should not be used on hardwood as it can cause it to split and crack, but spirit-based wood preservatives are quite suitable.
Periodically, exposed timber should be re-treated. Water-based stain-preservatives are useful for this as they give the wood a long-lasting colour in addition to deterring rot. They are not suitable, though, for the parts of a fence in permanent contact with the soil. The thin timber of which interwoven and close-boarded fencing is made is not quite so vulnerable as regards rotting because, provided it has a free circulation of air round it, it dries out quickly.
If you grow plants against timber fences, especially solid ones, they should be provided with a secondary means of support (plastic mesh, wires, etc.) so air can circulate behind and also to enable them to be pulled away from the fence so you can reach it easily for maintenance.
Timber, of course, can also be painted. White paint looks good on ranch fencing, but once you start painting wood it has to be done regularly. Certainly most forms of timber fencing look better with a natural or wood-coloured finish.
Check all wooden fences regularly for signs of rotting or damage and replace the defective parts as soon as possible. This could save a major repair job later on.
Plastic fences, netting, etc. Most plastics deteriorate gradually owing to the action of sunlight on them, but better quality plastic building materials have been specially developed to withstand outdoor conditions over many years. Ornamental plastic fences look better if they are washed regularly to restore their original finish, and should be checked occasionally for broken parts. The durability of plastic posts, imitation boarding, etc. depends largely upon the care given to its erection. Do not forget that plastic is inflammable and bonfires should be kept well away, especially from plastic-covered chain link, a fact which can be easily overlooked.
Wire fences. Fences consisting largely of tensioned wire between posts should have the wire re-tensioned from time to time as it is inclined to slacken off slightly.
Well galvanized chain link fencing should require very little attention for many years. Galvanized wire netting eventually rusts and, if a similar fence is still required, it will be necessary to replace the netting every few years. Wire netting fences are perhaps best used as a temporary measure, for example, while a hedge is growing up, then the need for periodic replacement is avoided.