When I first started distance riding I tried several different kinds of rear
interference boots, most leaving as much if not more dmage than I was trying
to prevent. Several years ago I started using the Professional Choce rear
ankle boots with very good results. You must make sure and put them on
snugly. I would say almost impossible to put on too tightly since there is
give in material with straight velcro closure with no leverage rings. I got
mine thru Running Bear, but I think other distance vendors carry them also.
Don't seem to be available in general catalogs that carry PC products.