Cob: rats?

[Mary Hooper]

Ok, say I eventually do get my vision of a cob house built and install black
flexible piping (which my honey swears by)to run water from the downspouts
carrying it from my metal roof  to the garden pond for cleaning by water
plants as I saw in a slide at a recent Organic Growers Conference in Flat
Rock, NC (yes, a plug for them. it was an inspiring event) So, say I do,
then how do I keep the mice from nesting in the pipe between rains? We've
had four years of drought here in the NC mountains and one wet spring does
not a drought-breaker guarantee......
Mary