If your fence is broken or has seen better days, you should consider your options to repair it before you make a decision to replace it.
Wooden fences: If part of your wooden fence has started to rot, you can replace bad slats, pickets or posts with the same type of wood, but the color may not match if the original fence has weathered. This is a job you can do by yourself or you can have a contractor do it. However, if 20% or more of your fence boards are rotted or in a state of disrepair, it is probably time to replace your fence. It is a good idea to weigh the costs and benefits of a large-scale repair against total replacement with a professional fence contractor.
Chain link fences: Chain link fences are very durable, but eventually they may start to rust. If the rust is limited to 10-15% of the fence, it is probably worth removing and replacing the rusted sections. If you plan to work with a contractor, get their opinion on the integrity of the whole fence, and get estimates on both the cost of repair and the cost of replacement.
Wrought iron fences: Wrought iron fences are expensive to buy and install. If you have a wrought iron fence that is rusting, it may well be worth having the rust treated and repaired. If you put the job off, it will only get worse and repair will no longer be an option. A reputable fence contractor should be consulted for repair jobs or advice on wrought iron fences.
Brick, concrete or stone walls: The expense and time it takes to install a brick, concrete or stone wall is very significant. Give careful consideration to repairs before you decide to replace, especially since replacement usually means removing the original structure.