A leaning fence is a sure sign that one or more posts need to be strengthened or reinforced. If the wood is completely broken or if the concrete is cracked or less than 3 inches thick, the post will need to be replaced. Otherwise, you can use wood reinforcement if the post doesn't have concrete or you can reinforce the post with a metal sleeve if the post is rotting or cracked.
Dig 6 inches below the bottom of one side of a fence post that is leaning using the shovel.
Attach a 2x4 to one side of the post using four wood screws and the screwdriver. The top of the new 2x4 should be at the bottom rail of the fence and extend to the bottom of the hole.
Repeat steps 1 and 2 for the other side of the post.
Straighten the fence, fill in the hole and compact the soil. Make sure the post remains straight.
Dig with the shovel to expose the concrete at the bottom of a post that is leaning.
Drive the bottom edge of one side of the metal sleeve to wedge it between the fence post and the concrete using the sledgehammer.
Pound the sleeve to rest vertically against the wood. Make sure the bottom edge of the sleeve stays wedged in the concrete.
Nail the sleeve into the post with the 10D nails using the hammer.
Repeat steps 2 through 4 for the other side of the post with the other side of the sleeve. Straighten the fence and replace any dirt removed.