The myth is that you can't lock the hubs if you can't move, but that's false. If your rear wheels spin in 4WD, then the front driveshaft, diff, and halfshafts must also rotate. When the halfshafts rotate within the auto hubs, the hubs will lock regardless of if the front tires actually move at all. This can be a problem if the spinning rear tires cause the rear end to dig deeper into the ground or to slide sideways on a hill and get you deeper into trouble.

Brent