J.G.
I found I like the "bobby" socks that roll down (or you can leave them up) from Old Navy. They also have rubbery bottoms that are now helping my 8 month old. She like to crab crawl and she can get better "traction" with them. You pay a little bit more than you would at places like Target but they do stay on. Lot's of times I'll find them on sale on-line for about 1.25 a pair. However, even these will wiggle their way to a little loose. But my daughter has never managed to get them completely off. I also liked their other socks that are a little thicker. Kind of like sport socks for babies. They are also tall with the rubbery bottoms. I'm not sure if the trick is the taller socks or if Old Navy figured something out but whatever it is it works. Now I just have to keep my dryer from eating them.
Good Luck!
Jen
http://www.mommysjoy.com