Thanks to all for your input. I didn't like the way the heel looked after the first part so I frogged and reknit without markers but found I couldn't distinguish the wrapped stitches--I'm using fingering weight self-striping sock yarn.
Then I resumed using markers; I had only the little plastic rings but they got in my way and drove me nuts. I switched to tied rings of button thread (all I had on hand late last night) and they worked a little better but I think I'll buy a ball of knit cro-sheen as Schurch recommends in her book. (Was thinking those tiny rubberbands the orthodontist used to make me wear on my braces would be perfect!)
I'm pretty sure I made some mistakes on the first part of the heel, so after I get my errands done today I'm prepared to face the music and frog it. The next step, the heel turn, looks scary but I have Silver's tutorial.
Assuming I don't go blind after this project, I'm hoping that once I become familiar with the technique, I can dispense with the markers. Sort of like taking the training wheels off the bicycle?
Have a great long weekend!