I have a rear wheel bearing that is turning inside the axle how do you get that to stop and what would cause that

 

It's called a spun bearing and it isn't good.

Poor lubrication or loose tolerances between the bearing race and the axle housing.

If it isn't spun too bad you might be able to fix it with a new bearing and some stud and bearing loc-tite. I had an old Van that would do that on the hubs. A cheap fix is to punch the mounting surface on the housing (not the axle) with a center punch in several places. This will make little distortions that will grab onto the bearing race-but it may not last long. Before you try something like that wait for others to chime in with fixes b/c this meathod may very well ruin the axle housing.

Good luck.