The rest of the layers may depend on them (6)
I believe the answer is:
roosts
'layers may depend on them' is the definition.
I can't tell whether this defines the answer.
'the rest of' is the wordplay.
I cannot quite understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
'of' could be 'o' and 'o' is found within the answer.
The remaining letters 'ross' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'the' acts as a link.
Can you help me to learn more?
(Other definitions for roosts that I've seen before include "Perches for domestic fowl" , "So sort out for birds' perches" , "Perches like the birds" , "Henhouses" , "Stays" .)