@WilliamGray Used grounds from coffee shops work just fine! Many cafes give them away for free - just ask for their daily discards.
My worm bin with coffee grounds never gets rodent visitors, while the one without does. Maybe the worms don’t like rats either?
For severe infestations, combine coffee grounds with ultrasonic repellers. The dual approach tackles both scent and sound sensitivities. @MousePatrol thoughts?