Old fences need to be replaced because of age however think before you decide to change it. Even though the boards are discolored and some are partially disconnected from the rails, the fence may still have years of life left. You may have to replace some rotted posts to straighten the fence and you may have to reattach some of the pickets, but it isn’t difficult to return the wood to something close to its original color. Restoring your old fence as an alternative to replacing it can save you hundreds of dollars.
Prop up the fence around a rotting post by wedging lengths of 2-by-4-inch lumber under the top rails and screwing them to the rails with 2-inch exterior screws. Cut the lengths of 2-by-4 so that the fence stands reasonable straight.
Backfill the hole with gravel or concrete mix, adding the backfill material incrementally as you check the level of the post with a spirit level. When the hole is filled to about a distance of 2 inches from the top, lay on concrete mix to form a small mound around the post so water will run away from it.
Wash the fence with a pressure washer. If the wood is moldy or extremely discolored, add deck washing detergent to the water, if your washer has the capability for it. If it doesn't, mix the detergent with water according to the specifications on the container and spray it on with a garden sprayer. Wash it off with the pressure washer.