This isn't seasonal but hopefully someone can help me.

I've been roasting turkey as a way to have a handy low-fat protein to grab for sandwiches and so forth.

I've carefully followed the instructions for defrosting in the Thanksgiving section but both times the turkey was not defrosted in the time suggested.  The second time today I made sure to use deep enough cold water to cover it, except it kept floating.

Should I try and weigh the turkey down with something so it stays submerged in the water?  Or should I just allow an extra couple of hours defrosting time?  Both turkeys weighed about 12 pounds so should have defrosted in 6 hours using the cold water method.