Eventually, fences break.

When they lean over, one way to react is to prop them up with a buttress.

Usually the wooden posts rot out from the bottom, just below the top of the soil.

If the fence is sitting on horizontal boards, sometimes called a weed board, those will rot first. They will be cheaper to replace than the whole rack of vertical fence pickets.

Even if every post is rotted out, the fence will usually stand up if you use a buttress.

Or three buttresses.

Or a whole row of buttresses.

Replacing the posts is the way to fix it properly, but that takes more planning and effort.

Another way to fix a falling fence is to attach some horizontal bracing with scrap pickets or firewood.

This fallen fence had an intricate fence picket protection scheme.

Each section had a continuous concrete support. I'm not sure what the channel was for.

Eventually the wooden posts broke.

Very rarely, the wooden pickets fail before the posts and rails of a fence. If the pickets are broken, it is probably because someone broke them.

Another quick fix is to install a new metal post to support the fence as it stands.

The most permanent solution is to rebuild the fence, perhaps avoiding the troubles which ruined the fence the first time.