Building fence is more challenging in rocky, frozen or swampy ground when it’s impossible to dig post holes efficiently, or pound posts. Michael Thomas of Thomas and Son Custom Fencing, at Baker, Idaho, says options in rocks include chipping or prying the rocks out with a hand bar, or using a hammer drill. “This works for drilling small-diameter holes into solid rock to insert a steel post, or even a bigger hole for a brace post,” he says.
“You can use either a pneumatic hammer drill that runs off an air compressor or an electric hammer drill and a generator. These work fairly well, especially if you use a heavy-duty industrial model. A small one won’t do the job in big rocks,” he says. With a good drill you can put posts into fairly solid rock.
In some terrain, where it’s not too steep and there are surface rocks, you can create an above-ground basket/cage of rocks as a brace to anchor the fence, in lieu of brace posts. Gather and stack the rocks and secure them with net wire, or make a cage and put rocks into it. “A cage three to four feet in diameter makes a solid anchor to secure your fence wire and stretch it from there,” he says. If terrain is too rocky to set wood posts, you can usually put steel posts into the ground deep enough to hold, using rock baskets every so often for braces.
Another strategy for rocks/frozen ground when using a post pounder is to use a metal “post” to create a pilot hole. The pilot post will often go down through rocky ground if it’s not solid bedrock, pushing aside the rocks, and will penetrate frozen ground, whereas a wood post would be forced out of line or shatter. Thomas uses a seven-foot-tall metal pilot post to create holes for wood posts in difficult conditions.
“The pilot post is only three or four inches in diameter and creates a hole to put the wood post into. The pointed bottom is solid drill steel about three feet long (to break the rock). Drill stem cone won’t hold up, but drill steel in the tip will break most rocks or push them out of the way. The rest of the pilot post is hollow, like well casing. This makes it lighter to carry. The top has a solid cap for the post pounder to hit. You drive the pilot post as far as you can, pull it out with the tractor loader, and insert your wood post into the pilot hole and drive it in — forcing it into the slightly smaller hole — and it is very solid and secure,” explains Thomas.
“If you are using an automated driver, the pilot post is handy to start the hole if you have to drive through rocks or frost, or tree roots. Just make sure you can pull the pilot post back out. Most of the automated drivers are already affixed to a loader or a three-point hitch that you can pull it out with. When you build a pilot post, make sure you have a way to hook a chain to it and pull it back out,” he says.