Why do fence posts lean in red clay?
Red clay holds water against a buried post and swells and shrinks as that water comes and goes. Each cycle works the post fractionally looser, and after a few wet winters the lean is visible from the house. The wood is rarely at fault. The hole usually is.
What actually makes a post lean?
Water in the soil, moving. Not wind, not the weight of the panels, and not the grade of the timber.
Red clay is dense and it holds water rather than letting it drain away. When it takes on water it swells; when it dries it shrinks and cracks. A post buried in that is squeezed and released, over and over, and each cycle opens the smallest gap between post and soil. Given enough winters, that gap becomes a lean.
Peachtree City takes about 50 inches of rain a year against a national average nearer 38. There is a lot of water moving through that clay.
Why does depth matter so much?
Because the deeper part of the hole sits in soil that moves less.
Surface clay swings hardest between wet and dry. Go down far enough and the moisture content is steadier, so the section of post down there stays where it was put and acts as an anchor against the movement higher up.
Thirty to 36 inches is the working depth for a six foot fence. A post set at 18 inches has almost none of its length in stable ground, which is why the shallow ones are always the first to go.
What is the gravel for?
Drainage, and it is the step most often skipped.
Six to eight inches of gravel under the post gives water somewhere to go. Without it, the bottom of the hole is a bowl in impermeable clay, and every rainfall fills it. The post then sits in standing water, which rots timber and keeps the surrounding clay at its most active.
The gravel does not hold the post up. It lets the water leave.
Does concrete fix the problem?
Not by itself, and this is where a lot of well-intentioned work goes wrong.
A concrete collar poured into a clay hole with no drainage underneath makes a sealed cup. Water gets in from above, runs down the outside of the post, reaches the bottom, and stays there. The concrete has made the trap deeper rather than removing it.
Concrete over a proper gravel base is a different thing entirely and works well. The order matters more than the material.
Can I tell how a fence was installed by looking at it?
Roughly, yes, and it is a useful thing to be able to read.
A run where every post leans slightly the same way has met a consistent soil problem across the whole line. A run where one or two posts have gone while the rest stand true points at those particular holes, or at something buried near them.
Gate posts lean first almost everywhere, because they carry a swinging load that the others do not.
Is it worse in some parts of Peachtree City?
The soil is much the same across the city. What differs is what has already been done to it.
In Wilksmoor, the newest village, a good share of lots sit on ground disturbed during construction. Backfilled and re-compacted clay drains less predictably than clay nobody has touched, which makes depth more important rather than less on a brand new lot.
In Aberdeen and the other older villages the problem is inherited. Fences went in decades ago, often shallow and often without gravel, and the leaning runs you see now are those holes reaching the end of their patience. Setting a new post back into that same disturbed hole repeats the original mistake with newer timber.
Braelinn adds a wrinkle of its own. Lots with golf frontage tend to slope, and water moving downhill through clay collects against whatever is in its way, which on a fence line is the posts at the bottom of the run.
When should a fence go in?
Autumn. September through November brings moderate temperatures and lower rainfall, and the clay is at a moisture content you can actually work.
Spring is fine too. What is not fine is setting posts into saturated clay immediately after heavy rain, and July is the wettest month of the year here. Clay worked wet compacts into something closer to pottery than soil, and it will not drain afterwards.
There is a temptation to book the job the week a storm has knocked something over. Waiting a week produces a better fence.
What should I ask a contractor?
Two questions, and they take ten seconds.
What depth are the posts going to, and is there a gravel base under them? An installer who works this soil answers both immediately, because they are the decisions that determine whether the fence is still straight in fifteen years.
Everything else on a fence quote is about how it looks. These two are about whether it stays up.