I tried to explain this before and don't think it went well. I finally got around to making a video, a picture is worth a thousand words. Since I started doing this I don't have ladder problems.
I'm also working on a complete tutorial for double knitting 2 socks at once. If you're interested in that check out my other videos. Right now part 1 is up, transfering the cast on, joining and the ribbing. It will probably be at least another week or two before I get enough for part 2 with the leg, heel, turn and gusset.