Rodent proofing engine compartment

[cmac2012]

One of my best clients has an '08 S550. He lives in the semi boonies of Woodside, CA. A not small number of horses live not far away. Leads to rats - all the horse feed lying about.

He recently lost the main upper radiator hose to serious rat chewing. During the course of replacing that they discovered another hose nearby that had also been ruined. He says the cost was $600 each (!??!). Is that for real? From what I could see of the upper hose it had a hose clamp sort of setup that I had not seen. Looked like a special tool was needed.

We're trying to somehow ratproof the engine bay. Closing it in with that strong 1/4 inch square wire mesh prolly won't work. I found an exterminator online who swears that peppermint oil will keep them away. Also black pepper is touted. I've read the opinion that leaving the hood open while at home will make the engine bay less attractive to rats. Seems quite the drag to open the hood every time you come home.

Any great ideas?