The depth of your fence posts will be the single most important issue in building a fence. It will determine how long your fence remains standing.
A simple rule is, height of fence, divided by 2. 4′ fence, posts need to be 2′ in the ground. And so on. Soil conditions determine depth of hole, but in my case, I have a Kubota tractor with a Belltec auger. That means I can dig through 5′ of solid rock, with up to 8,000 pounds of down pressure. That far exceeds anything a Bobcat or conventional tractor and auger can do. The bottom line is, there’s a means to get the job done right.
A 6′ privacy fence with posts 18″ deep will blow over during the next storm. The average customer spends over $5,000 on a privacy fence (300′ backyard), take the time and ensure you’re getting what you are paying for. Not that you need to eavesdrop or spy, but ask questions. There are a lot of fly by night, or wheel barrow and bucket guys as I call them, out there ready to pounce on your naivete. I mean no offense by assuming your naive. I’m simply trying to help!
This rule does not apply to ranch fence. 4′ post depth minimum is needed for all 4-5′ fences, and 5′ depth for all game fences (wildlife). We will get into field fence tomorrow, so stay tuned.