How to keep away small cats from entering engine bay?

As the title says, this is the 3rd time in last 2weeks where i’ve seen small cats entering the engine bay from beneath and staying there for eternity until i forcibly make them go away. In case i turn ON the engine by mistake what can be the consequences? What damage can cats cause to the engine or wiring by chewing it? Is there any way to keep cats away or i should manually keep checking for them before starting the car?