as mentioned, mothballs work well (they do evaporate eventually) also those urinal deodorant containers (cake) work wonders too. when left outside, i'll cover tractor w/tarp & open hood as rodents generally shy away from nesting in light. ever pass by vehicles in rural areas w/hoods open? that's the reason also frequently moving the location will help to confuse them too..... don't let them get to the wiring harness or intake filter!