A discrete bit of string/orange cord in trat's strikes me as a good idea, especially if it's possible to clean the crud off the rest. Most damage, though not all, will be caused by passing cavers who don't see the "best" route, rather than by deliberate vandalism, and for myself, I'm always happy if a single route is marked clearly to prevent me causing damage before I see what's being conserved. The orange cord really isn't that intrusive.