Resnick:

 

I always wondered why someone hasn't come up with a rodent deterrent to put in insulation for cables etc at the time of manufacturing.

 

Ministry of Education specify that for network cabling below 500mm under a floor that is must rodent proofed (fully encased in conduit) or gel filled. I don't really get the point though - by the time the rates get to the gel they are already at the wire so chances are the actual copper is damaged anyway!