i've always put 3-4 layers of duct tape on the edges of my tips, starting about 12' from the tip. A 1/2' wide strip is good enough, most chipping occurs on the very outside edge of the topsheet. It works great, looks like crap, and makes my skis less likely to be stolen so overall , it is good. I also think that if you put a bunch around the edges of the tip, it might help absorb vibrations and reduce the chance of delaminations... just a theory but It has worked for me!
Critical Motion Films