One side of my fence has been deteriorating for years and leaning towards my side of the property. When I was out of the country, my friend came over and propped them up with some 2×4’s to keep it from falling. The posts appear to be set in dirt and not concrete so the proper repair is to replace them which would require rebuilding the entire fence. You can actually pour the cement mix dry and water it after which makes it a bit easier.
I came across the Simpson Fence Mender at Home Depot in the joist hangers section. I bought one to try it out since they were relatively inexpensive. The instruction indicate it should be installed in pairs but I figure a single one should improve the post.
The instructions indicated you should hammer on the indentation to drive it down but it is kind of hard to hit it with a mallet. I just used a scrap piece of wood and pounded it from the top keeping it as close to the post as possible.
It actually worked pretty good and it was secure enough to remove the bracing and I bought a second one for the neigbouring post.