My socks develop holes on the underside of the heel, right in the centre. Most heels have no reinforcement there, so I have been pondering the best way to pad that spot without making the sock hard to knit or uncomfortable to wear.
I read that you could work an ordinary gusset heel on a toe up sock, with the reinforced flap on the bottom of the foot instead of at the back of the ankle.
It took a few tries (because I'm still fairly new to gusset heels) but it actually works!
You make it like any other toe up sock: start at the toe, knit the foot, smooth on the sole, patterned on the instep if you want (mine's ribbed). When you get to the spot on the foot where heel meets arch, you make the heel flap, turn the heel, pick up the side stitches, resume knitting in the round and decrease your gusset stitches away over the next few rounds. In other words, you do exactly what you'd do for a heel if you were working top down, and you end up with the padded bit on the bottom of the foot, with just a little bit of reinforced stitching up the back of the heel. I can't see any reason why you couldn't keep the slipped stitches coming up the back of the foot if you get wear there from your shoes, but since I mostly wear clogs or slippers or just my socks, it's not where I get holes in my socks so I don't bother. That's why I liked this: it puts the reinforcement where I need it, and doesn't require me to do any extra thinking or planning!