Advice for winter storage of mill ?

[apm]

I like the bottle trap for vermin. However, my wife would object!
We live in an old stone built house (1730 or so) and every year the local Mice came in to overwinter.
Set lots of traps, but when you find droppings in your breakfast cereal it was time to take further action.
We bought a couple of ultrasonic Mice chasers.
They just plug into your power sockets.
NO MORE MICE!
I also have one that operates with a couple of PP9 batteries that I use in my RV when it's not in use. (Like this year. It's been in storage since last October)
Our "Jacko" mill lives outside all year. The power head, hydraulic engine and controls are all covered and the main bed is sprayed with oil.
I remove the batteries and keep them on a maintenance charge over the winter.
It was built in 1995 and still earning its keep.

which ultrasonic Mice chasers did you buy? We've tried some, but had no luck. 
Greg