Four by six treated post failed in May, 2018, probably because one of the horses put his butt to the fence to scratch it. Installed October 2103, replaced 12/28/18.
Step 1: Gather tools and materials. Best way to carry eighty pound sacks of cement to the job site? Your tractor.
Step 2: Dig the hole. The fence tells you where.
Step 3: Check depth of hole. Top of post should be at top of fence, in this case about 64″ above grade. Hole should be deep enough to place a few inches of gravel at the bottom so the post does not rest on soil. Don’t cut the post, dig the hole deeper.
Step 4: Use a level to plumb the post. Mix the cement and place in hole. In this photo, a wood block braces the new post against the old concrete.
Step 5: If your pipe panels have loop legs, be sure to press them into the concrete before it hardens. Make sure the depression can drain into the surrounding soil. Top of concrete should be slightly higher than grade, so rainwater runs away from the post.
Step 6: Secure the fence to the new post. A U-shaped metal strap with two 1/4″ lag bolts should work. You can see one near the top of the first post in this photo. The new post is next in line.
In this corral, the pipe panels are supported at every other junction. Steel rods were pounded into the ground where not supported to keep the horses from pushing those sections out (the pinned joints act like hinges). You can make the rods from #4 rebar or larger. Drive them in on the outside of the leg until flush with the top of the loop.
Technical note: The 4×6 posts in this corral were oriented with the broad side facing the pipe panels, to accommodate the U-shaped straps. The posts would do a better job of resisting the horses if their narrow side was put toward the fence. But you’d have to find another way to secure the panels to them, such as drilling holes through the vertical members and lagging them directly to the posts. Straps have more ‘give,’ which is nice when horses lean against the fence or ground conditions change from wet to dry. The face-to-face spacing between 6×6 posts on a 12′ gate can change 1/4″ or more between summer and winter in this area.