Snake for Pest Control

[hhw]

Alright, I have way too many pests on my property now that there are no longer coyotes in the area. I've always wondered whether a snake can be used instead of a cat or a terrier. Especially, since it would digest the bones there would only be snake poop and not carcasses lying around.

It should eat
-rats
-if possible, european grey squirrels (those nasty invaders keep getting into the attic)
-skunks and crows would be nice too, but I think that'd just be dreaming
And not eat non-pests like small birds, etc...

Now, other important traits I think would be:
-stays in the house/area
-tolerate lower temperatures enough to be active most of the year (this is Vancouver weather by the way), or be smart enough to stay inside when it's cooler
-extremely secretive (staying in the walls), and therefore nocturnal I suppose, so relatives and neighbours won't see it and get hysterical

So, I'm thinking a good sized colubrid like a rat snake or bull snake might do the trick.

Any suggestions and reasons supporting them?

Also, is this actually feasible or is this just wishful thinking on my part?