Difficult keeping old, small squirrels away (6)
I believe the answer is:
hoards
'squirrels away' is the definition.
(I've seen this in another clue)
'difficult keeping old small' is the wordplay.
'difficult' becomes 'hard' (synonyms).
'keeping' is an insertion indicator (some letters kept inside).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'small' becomes 's' (abbreviation - e.g. clothes size).
'hard' enclosing 'o' is 'hoard'.
'hoard'+'s'='HOARDS'
(Other definitions for hoards that I've seen before include "Squirrels away" , "Stockpiles" , "amounts of treasure" , "Accumulates" , "Gathers together and saves for future use" .)