Very keen to employ old dodge (5)
I believe the answer is:
avoid
'dodge' is the definition.
(I've seen this before)
'very keen to employ old' is the wordplay.
'very keen' becomes 'avid' (I've seen this before).
'to employ' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'avid' enclosing 'o' is 'AVOID'.
(Other definitions for avoid that I've seen before include "Refrain from (something)" , "Evade - escape" , "Miss" , "Sidestep" , "invalidate" .)