The best way to prevent rodents is to remove all food sources and seal every entry point. Use steel wool to plug small gaps in the hull or vents, as mice cannot chew through it. While scent deterrents like peppermint oil are popular, the most effective defense is a solid steel structure with a tight-fitting door. Elevating your boat on a trailer inside a metal building makes it much harder for pests to climb aboard compared to a boat sitting outside under a plastic sheet.