Be found as old dog going round about (5)
I believe the answer is:
occur
'be found' is the definition.
(I've seen this before)
'old dog going round about' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'dog' becomes 'cur' (I've seen this before).
'going round' indicates putting letters inside.
'about' becomes 'c' (abbreviation for 'circa'**).
'cur' enclosing 'c' is 'ccur'.
'o'+'ccur'='OCCUR'
'as' acts as a link.
(Other definitions for occur that I've seen before include "Come to pass" , "found" , "crop up" , "Befall" , "appear" .)