Hi rego, When I lived at our old apartment, we had mice problems. Steel wool is what I used to plug up holes in walls or by pipe openings and anywhere there was a hole, small or big. Moth balls I threw everywhere in closets to cabinest. They wont harm anything. Just a heavy smell to moth balls. Also, mice do not like dryer fabric sheets. We used V-traps as well and worked good. They also have electronic ones which caught the mom of the mice too. So, throw moth balls in attic, it wont hurt you or anything. Throw some in walls to if you have an opening but then put steel wool in hles like I said. They wont go thru steel wool. Ok. hope it works for you. good luck, kim