We used to have a neighbors cat that would jump up and sit on the outside of our windows which drove our cat crazy. Based on advice from others, I crushed several cloves of garlic, added water, and let it set for a day. A couple squirts of the garlic water at the cat through the screen and viola - no more cat visits. If you need a longer shot for the garage, a squirt gun or small super-soaker may be a better delivery system.