How to prevent freehub body damage? I feel like this is poor design. I have two wheelsets that are less than a year old which have damaged freehub bodys due to cogs digging in to the splines on the freehub. It's so bad that I can't remove the cassette spacer without filing down the splines. I had to use  pliers and chain whip to remove the cogs that were embedded in the freehub when trying to remove the cassette.

Most of the damage is on the center of the cassette as the largest 3 cogs are held together by carrier. I'm using a shimano 105 cassette and  Novatec disc hub and Velocity ATB convertible disc hubs (which were somewhat damaged in the same fashion, but not as bad as the novatec).

I'm using this bike for cyclocross, offroad exploring, light singletrack use, Rail trails and some road riding.  

How can I prevent this damage to the freehub from happening?
From Stan's NoTubes FAQs on wheels and rims:


  Why is my cassette digging into my freehub body?  
  
  Stan's freehubs are made lightweight using aluminum like many other brands.
  We recommend using cassettes with a rigid alloy
  carrier (XTR, XT, XO, etc. - Figure 1) for the largest sprockets.
  Cassettes with individual cogs (Figure 2) may mark the
  alloy freehub, though marks are only cosmetic and will not affect the
  performance of the hub.


From your picture it appears the freehub takes the hit from the individual sprocket. 
Need the cassette to act as a unit and spread the load across all sprockets. 
Tighten down more or look for cassette that has more of a body across the sprockets (rigid alloy carrier).

See how the rigid body (left) shares the force across not just the sprockets but also between the sprockets.