I've not noticed any problems with stones, but the gravel in the drive and the road outside is 20mm grid, rather than pea gravel. However, I see nothing wrong with a round track and shaped rollers. I think it would also be potentially a lot more difficult to damage.
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It is simply around the end, so it could, in theory, be lifted at the open end. However, I don't see that would gain much, except perhaps being able to dislodge it an inch or two sideways from the track at the bottom. The other end has a steel bar over it, which carries a pair of guide wheels (and which sticks out too far, so that I hit my head when I am lubricating the driving rack), and that end wouldn't lift. Given the weight of the gate, I suspect it would take a small crane to lift it anyway.
There is a beam across mine too, between the gate pillars.
Its very nice to be able to push a button and watch the gate roll back (and another to watch the garage door go up) when the rain is tipping out of the sky. Given that this my place in the sun, I've seen far too much rain there.
Colin Bignell