Originally Posted by bmthom.gis

#1 - work on your cornering. Follow through when you turn. If going through sand, if you need to scrub speed, do it before you hit it (though the sand will scrub speed off for you). Just think of it like driving in snow or mud. Don't add or subtract power/speed during your turn or in gravel/sand. We have a lot of sand where I live (like, a lot. Where does it all come from???) and I always find myself riding through it.
#2 - If you can go wider with your tires, go wider. Wider tires = lower pressure = better traction

Why are your wheels locking up?

I don't use Contis. I've heard so many mixed things about Gatorskins and their traction (or, lack of). Personally I prefer Panaracer, or Clement or Vittoria tires.