A few weeks ago I helped my neighbor add onto his pasture. I don't recall the brand of the auger but with a John Deere 4000 farm tractor in rocky hard soil there were some tough spots.
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Instead of using t posts he used smaller wooden posts. The tractor
auger too big. He ended up renting a skidloader and small auger from the local hardware store. He said he should've done that right away.
I'm in the same boat. You can find older augers for 100 to 400 on auction. I like to have items I need " just in case" . For rental prices I could buy one and have it sit. At the same time the rental store is storing it, and maintaining it. Sometimes it's just easier to rent or hire a neighbor.