[QUOTE=Lalwendė] 
Wouldn't a ranger defend during the day someone that they were going to defend in the night? Sorry if I've not grasped the concept of that yet, but I'd have thought that's what would happen?  

  Or am I getting 
Rangers mixed up with 
Cobblers? I don't know.
QUOTE]
Since rangering is the gifted role I have been relatively successful in I would say no.  The point of being a ranger is to protect those you think the wolves will kill.  Boromir would have been a low priority at that point if someone has attracted suspiscion the wolves will hope the  villagers will do the job for them.  Later when Boro declared himself as  hunter there might have been a case for protecting him long enough to pick a good target.   And with 3 rangers the added dynamic 
Lommy pointed out comes into play - not only do you have to second guess the wolves but second guess the other rangers.