A fence is only as good as its posts. Wind, shifting soil, falling trees and other blunt impacts can cause posts to fail. Once a fence has completely fallen, the only lasting repair is a complete re-installation of the posts. Posts and other fencing materials that are not broken or rotten can be reused. Do not reuse old concrete that has shifted, as it can rarely be reset firmly. Detaching the fence panels from the post makes resetting the posts simpler.
Lay the fallen section of the fence down with the picket side up and the posts toward the ground. Remove any screws from the panel faces with a cordless drill driver. Stack the fallen panels for reuse.
Break any old concrete from the post bases with a 3-pound hammer and brick chisel.
Remove any old concrete or broken-off posts from the fence-post holes. Dig the hole out to its original size and depth. Ten to 12 inches across and 24 inches deep is typical. The original depth can be determined by measuring from the bottom of an old post to the ground line.
Replace any broken, rotted or badly damaged posts. Set one post and a half bag of concrete in each hole. Start at one end of the fallen fence.
Add water to the first hole and mix the concrete with a scrap of lumber. Use a level to check the post from front to back and side to side. Adjust the post to center the bubble in the level indicator, and pack the remainder of the hole with dirt to hold the post upright until the concrete hardens.
Reattach the first panel by lining up the edge of the panel with the outside of the post. Drive two 3-inch treated deck screws through the face of the panel and each horizontal rail into the post face with a cordless drill.
Stand the second post upright and line up the unattached edge of the first panel with the center of the second post. Attach the panel with screws as for the first edge. Add water to the concrete and mix it. Pack the hole with dirt.
Add the second panel butted up to the first in the center of the second post. Attach the panel with screws as for the first panel. Continue attaching and adding posts and panels using the same technique until all of the fallen fence panels are reattached.