I am a huge sock knitter, knitting one as I type, yes almost at the same time. I know there are double heel patterns that one knits in while maming the sock, not replacing it once it's gone. I have to learn this as my sister's keep falling apart at the heel. I am a toe up pattern lover, but taking advanced lessons in toe down to learn new strategies. I've knit forever but one can always learn new things. P.S. There is a youtube video on reinforcing socks and toes. I just looked it up.