At that point I would just not build a fence.
Mine ended up 330 feet including the 60 I had already ran. Rented a 1 man auger from home depot. Out of 27 holes attempted with the auger, it worked well for about 6 of them. Another 6 or so it worked ok if I ran it for a bit, filled the hole with water, did some other work and came back to it after soaking. Some required a few soaking cycles because 30 minutes after pouring 3 gallons of water into the hole, 6 inches below the surface was still bone dry. The rest it would hit a root and just spin and not make progress, or would grab it and take me for a ride. Twisted my right arm pretty good on one of them; took me a good 30 seconds for the pain to subside enough for me to decide it wasn't dislocated. Had to cut a few roots with a sawzall. All of them had to follow behind with the clamshell diggers for the last few inches. Had a couple times where I had to disconnect the motor and screw the auger bit back out of the ground. All in all I'm not sure it saved me any time over the clamshell diggers, it just used different muscle groups.
All the holes are dug at least, but I have 3 more posts to set. I miscalculated my length and came up short by 2 line posts, but I have 2 extra gate posts because I was able to re-use the posts from the gate I took out. Just have to drill through the post to make holes for the rails but my drill battery only made it through 2/3 of one post.
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I counted 48 trees inside the fence.