Over the winter, a squirrel got into my 30 X 40 shop, which has a drop ceiling under a pitched roof, metal building.
Obviously can get in & out from somewhere besides doors.
Spent the day up there moving boxed stuff to totes & cleaning up.
Found 2 holes big enough leading to ridge vent; covered the holes with wire mesh.

No sooner get done, cut up the old boxes, clean up, then I hear him running back & forth on the drop ceiling.
He wasn't up there when I was.

I've tried the powder they supposedly hate, the high-frequency plug-in, no success. I feel like Bill Murray.

I'm open to ideas, what works ?