I'm looking for a couple of half-rounds, basically big poles that have been cut length-wise in half, to use as ground lines for my ditch. I've checked a couple of garden centers and Home Depot. Any ideas?
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Find someone with a table saw and have them split a large
round rail. Or maybe get a 6x6 and cut it diagonally so
you will have two triangular pieces and take the top off
the triangle with a belt sander or a table saw or could be
done (tediously) with a rasp.
Contact your local utility company about getting retired power poles. They're usually free, though you may have to go get them. Then find somebody with a chain saw to cut them. Or just bury half to reinforce the edges of the ditch.