There area direct bury Cat5 cables, though I don't think I've seen a rodent resistant one like I have the telephone cables. But like Skip says, the direct bury Cat5 should help. It is gell filled, wrapped in some plastic stuff, protected by a copper shield, then a heavy poly jacket.
I've never direct buried Cat5, we run it in conduit anyway.
Good Luck!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com