Finished this belt a little over a week ago. I had these balls of hemp beading twine sitting around forever and just decided one day to knit them into a belt, so I grabbed some number ones and knitted a few inches in stockinette for the buckle then did a basic six stitch cable with two stitches on the side and yes, I actually wanted them to curl up. I should have used three balls, one yellow, and two green, one for each side but for the sake of laziness, I carried the green behind. For the part that goes through the belt, I decreased by two and did it stockinette with a double garter stitch (sl 1 kwise, k 1, k2 on end) selvage to hopefully keep it from curling but it didn't work: the selvage was tighter than the stockinette which I didn't think about because it never mattered before but in this case, I have to pull it tight since its a belt and that winds up curling it up after just a few pulls. The twist from the cable also doesn't make things any better.
Its not perfect, far from it, but its the first thing, aside from scarves, I've knitted up without a pattern, so for that, I'm proud of it.
I'm definitely going to have to make a second one: this time maybe with a real hemp yarn so it'll look less twiney, using three balls, putting a purl row right after the end of the cable to help neutralize the twist, and with a stitch that won't curl when pulled hard.