Righting a leaning post and rail fence?

[fireweed farm]

A friend is keeping a Clydesdale here in my paddock built of wooden posts and wooden rails.
Because it's so big it is able to reach over the fence and eat the tall grass. Doing so it's caused the post and rails to lean in, and fairly significant.
We are now mowing around paddock and making sure it has surplus feed, but I'm curious how exactly best to right these posts so that they aren't permanently loose?
The ground is pretty much clay so posts will move somewhat when wet. Without fixing these correctly I'm betting even if we right them now, they're going to lean during next springs thaw.
Trying to remain relaxed but huge investment in fence here.
Thanks!

[Bearfootfarm]

but I'm curious how exactly best to right these posts so that they aren't permanently loose?

It won't do any good to fix them until he stops the leaning, which can be solved with one hot wire along the top of the fence.

After that, just straighten them up and tamp the soil in place
You may have to add some dirt to get them tight again

[fishhead]

You might try digging on the side you want to move the post to and then filling the gap it makes when you plumb the post with gravel. That should help prevent it from returning to the leaning position.

I'd also second the hot wire on top and maybe remove temptation by mowing the grass on the outside short.

[fireweed farm]

Yes the hot wire has already been started. Very thankful to not be reading "too bad once leaned it will remain loose".
Thanks for the help!

[agmantoo]

Get the post upright

On the side that the post was leaning toward dig a horizontal trench about 8 inches deep and the length and width of a treated wood post. Go for a snug fit to where the post width just fits the hole.

The trench should be centered on the post that is leaning. Lay a treated post horizontally in the trench and firmly against the post that was leaning. Tamp the soil tightly to hold the horizontal underground post against the post you are correcting. Throw a few handfuls of grass seed in with the last dirt being used to cover the in-trench post. You will have created a braced post that is now being held upright by the underground buried post. The post arrangement will resemble an upside down Christian cross with the top and crossarm underground. This is a great way to install clothes lines to keep the post from leaning also.