Heard running round the lair and got set (8)
I believe the answer is:
hardened
'got set' is the definition.
(I've seen this in another clue)
'heard running round the lair' is the wordplay.
'running' indicates an anagram.
'round' indicates putting letters inside.
'the lair' becomes 'den' ('den' can be a synonym of 'lair').
'heard' with letters rearranged gives 'hared'.
'hared' going around 'den' is 'HARDENED'.
'and' is the link.
(Other definitions for hardened that I've seen before include "describing some criminals" , "Toughened" , "Rigidly set" , "Experienced, tough" , "Inured" .)