After 27 years of having indoor-outdoor cats, the last one died in May 2015. (We now have only an indoor cat.) During those 27 years, we never had a problem with mice.
During Snowzilla (Jan 2016), the storm that dropped over 29 inches on our area, we sprinkled bird seed under the eaves of our house, in addition to shoveling a space on our patio and stomping snow-shoe trails to the bird-feeders. At least two mice came in through a space created by the installation of a new heat pump.
Sixteen trapped (and released) mice later, and with the entry space stopped up, we thought the problem solved. A few months later -- more mice -- twelve trapped, plus one eaten by the indoor cat. Now, another two months later, more mice.
Short of getting another indoor-outdoor cat, what do you recommend? What would be ideal would be a spray for the outside that would smell like a cat, and would fool the mice. We leave no food outdoors, except for in the bird feeders, which are 100 and more feet away from the house. (We live in a semirural area.)
And, why do you suppose we were free of mice for 8 months until the aftermath of the big snowstorm?