Group of devout dudes in rubbish skirts (7)
I believe the answer is:
borders
'skirts' is the definition.
('border' can be a synonym of 'skirt')
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for borders that I've seen before include "Boundary lines" , "Perimeters" , "Decorative edges" .)