Driveway markers/reflectors

I have a 300' driveway that has a sharp right turn in it at about 200'. For a good portion of the rest of it there is a 3'-4' drop on one side. I can't fill on that side because the driveway is already under the drip line of a 150-250 yr old Bur Oak. Bringing in fill would damage the tree since oaks are notoriously sensitive to fill put on top of their root system. Along the drop I have built a fieldstone retaining wall that I am happy with.

Now my problem is I need to mark the edge of the driveway. First of all I need to make sure that noone goes off the edge. (Already had the mail carrier do that.) Secondly in the winter I lose where the driveway is when the snow drifts.

Most driveways markers I've seen are ugly. Also most of them aren't tall enough. I need the reflectors about 5' above ground. I've seen some nice leaf ones online at Hansen Ironworks. They're somewhat expensive, but I think it's important that they add not detract from the landscape. I would eventually like to run lights along the drive, but that will be several years down the road. Do you have any ideas? Do you know a good source for attractive markers?

Thanks,
Jerger