Start at ground level
Check door frames, gaps beneath gates, drainage openings and where pipes or cables enter the wall. Rodents can pass through surprisingly small openings.
Move up to eaves and voids
Roof edges, ventilation gaps, air-conditioning penetrations and service voids are common routes into ceilings and walls.
Look for the signs of use
Grease marks along a wall, droppings, gnaw damage, nesting material and a worn path through dust or vegetation all point to a route that is in active use.