Cats, it normally stops them ever coming into the house again, only problem is if the cat catches them, my daughters cats (3) normally play with them, never hurts them, unfortunately though they die of fright.

She doesn't have mice but her friend next door did so she loaned the cats out for a week.

To be honest don't think there is any real humane way, on the lighter side; you could feed them then they may die of obesity! Well it's almost a natural death.