To be honest, I think the only way to keep them from locking is to twist my way. Don't mean to sound big-headed but I have tried to twist the way a lot of people do it, which is just wrapping two sections of hair around each other without doing anything else, and it looked like a recipe for tangles. If I keep my hair twisted, I hardly ever need to spend time detangling because my hair NEVER tangles or knots up. I keep my twists in for a long time BTW and wash twice a week, and except for the occasional few that might unravel, I have the easiest time with my hair.
My twisting method differs from others by the fact that I first twist each section/strand clockwise on its own before wrapping them around each other anticlockwise. This ensures the hairs in each section stay in their place and don't get tangled with those in the other strand. Undoing is also very easy as all I do is unwrap and then untwist each strand separately and hairs just separate with ease.
I will also add that I don't use products when in twists--but I don't know if that makes a difference at all. Mwedzi, who uses products, tried this twisting method so can tell you if products made her hair stick together or not. But while she hated how skinny the twists looked, she found they hang longer and I think she said they didn't unravel when she washed. She didn't like the twist-out though from them so if a twist-out is what you plan to rock later on, just know the twist-out looks more like crimped locs--you've been forewarned.
All in all, I don't think she was disappointed by the method. It does take long until you get used to it, when you can do it faster.
Anyway, here is a demo of my twisting method:
http://www.youtube.com/watch?v=5-PPsh1_Np0
And here's a demo of how easy it is to undo the twists even after several washes:
http://www.youtube.com/watch?v=Jff-Uqfb_SA
My twists after 8 washes in 4 weeks (sorry I forgot how huge the pic is
):