Almost always the post, almost never the wood. North Texas sits on expansive clay that swells when wet and shrinks when dry, and that annual movement works a shallow or narrow-set post loose a little at a time until a wet season finishes it.
Blackland Prairie clay, the black gumbo under most of Dallas, changes volume with moisture. Through a wet spring it swells and grips; through August it shrinks and pulls away, leaving a gap around the post. Repeat that for a few years and a post that was set shallow has been levered a fraction further each cycle.
Sprinkler heads soaking one stretch of the line keep that soil in permanent swell. Large trees nearby pull moisture out on their side and tilt the balance the other way. Slopes concentrate water at the bottom of a run, which is why the low corner usually goes first.
Sometimes. If the pickets and rails are sound and only a few posts have moved, resetting those posts properly is a real repair. If the run has been leaning for years, the framing has usually racked out of square and standing it back up on the same posts just resets the clock on the same failure. We will tell you which one you have.
You can, and it is the most common false economy in this trade. The post that failed is the post being re-used. Unless the post itself is sound and simply came loose, it will fail again on the same schedule.
Not if the footing is formed so water drains away rather than collecting in a cup around the post base. Bad detailing, not concrete itself, is what rots posts.
Deeper than the code minimum, which is the point of our whole approach. The full answer, with the reasoning, is in our guide on fence post depth.
We walk the property, give you a straight price, and show you how it is built underneath.