yeah my LS sometimes is parked for long periods, and one day i found debris and feces under the car right in the middle. since the car is pretty much sitting on the ground due to my air suspension, i suppose a rodent made a nest in the heatshield area above the driveshaft. left a trap out and never caught the bugger. drove the car and it never returned.
best way to mitigate such a nuisance is to set out traps, keep the yard clean, get a cat/dog, and drive the car often!