Lets start by saying that I rent and do not want to invest money into moving the fence post, I am looking for a cheap fix.
About 150 feet of my fence is leaning. The reason is the post are put in an area where it is very very wet. The post are not rotten but the ground is very soft. The post are supported somewhat by a wood brace pushing them straight. This is not workng as the braces are sinking too. Is there a way we can straighten the post and put something in the hole to secure it? What about sand, rocks, ready mix? It's not a big deal as there is a hot wire to cheap the ponies in but it looks like crap. None of the boards are even and the post tops are all dfferent heights.
......................Pull a Nylon stringline and stretch it from the first post too the last post . Do this by driving a nail in the center of the post on TOP and stretch too the last post . This will give you a line too Align all the other posts off of . Now , I obviously can't see your fence so I have no way of knowing how far out of kilter the first and last post(in the 150 foot span you referred too)......ARE . From this stringline I would try and remove and reset each post . Judging from your description I'm thinking cement is the only way too anchor the posts in the ground . If the fence is made up from panels you can try and detach each panel , clean out the hole , maybe deepen a bit and cement it back into place . I'd also want the bottom of the panels off the ground a couple of inches too keep them rotting away . Lots of work but worthwhile if you have the time and energy . , fordy