M.P.
My exterminator said the best way to prevent mice is to find where they are coming in and close the opening. You may have to hire an exterminator once to find these places. They are trained to look out for possible entry points-places you would never suspect. You will be amazed how small of an opening they can squeeze through. Anyway, this could be an isolated event. But if one got in, another can.
Hope this helps.