Critters under the hood

#1

Any suggestions on preventing mice or whatever(I never see them), from nesting under the engine cover on my Kia Rio? The car was recently running poorly, and when I took the cover off to check the plugs, the plug wires had bee chewed up by varmints. After replacing the wires, I recently rechecked and found another nest.in the same place.

#2

I had the same problem and my mechanic told me to put moth balls under the hood.