Hello,
I think there might be a correlation/causation issue here. Sure, there might be fine sand there, and yes, the unserved wire might rust, but the two might not be related. Why bring in a dubious sandpaper mechanism when higher temperature and salinity can account for the problem? It has been a while since I looked, but in the past we've had some success with commercial coatings for wire. The trick is to find a supplier who will sell by the quart, instead of by the barrel. The stuff tends to be nasty, but pretty effective. The wire won't be immortal, but it will last longer. You might try contacting these folks:
http://www.industrialpolymers.com/cu...kB6BoCtFzw_wcB. Maybe they'll steer you towards a distributor.
Fair leads,
Brion Toss