Alan, that's a problem (and can be a costly one) with a painted hull. Those soft fender socks are nice as long as they never touch a bad surface, so they are worth getting as long as you keep an eye on them. But the best solution is to spread the wear, using more fenders, or fenderboards/pads. I've seen exercise mats used for that, they aren't as tough but they are inexpensive.
You may be able to lessen the wear by spraying a wax-type lubricant on the fenders and waxing the hull, since the wax will take wear before it gets down to the paint. Anything that is paraffin or simple "wax" like a mold-release spray (on the fenders, not the hull) may help some. And washing
down that side with fresh water
, because it may be salt
crystals on the hull and fenders that are doing the real wear. They CUT just as well as any fine abrasive.