Along with the installation of Auto Tack Mat in the engine, consider one or more complimentary strategies that may be helpful depending upon your circumstance:
Leave the hood of the engine open at night, thereby reducing the warmth and shelter aspects of the engine compartment. However, some weather conditions (including rain or snow) will preclude this strategy, and the privacy of your parking location will also be an important consideration (avoid visible areas such as public streets).
Place scented items in the engine. Some vehicle owners have found this to be helpful and others have not. Rodents have a keen sense of smell, and certain scents that humans may enjoy are objectionable to rodents! Examples of scents that reportedly discourage rodents include peppermint (from concentrated peppermint oil) and certain pine-scented products. Another scent-based strategy is using dryer sheets (they can be folded into a strip and tied around items in the engine). One of the drawbacks to scented items is the need to frequently refresh the scent.
Placing rodent traps, glue mats, or other similar devices in the area surrounding the vehicle where rodent droppings are present may also be helpful. We are not always aware of “hidden” locations in our yards that demonstrate rodent occupation, so take the time to look around and set those traps!