Shelter here finally protected by DM's successor (3)
I believe the answer is:
den
'shelter' is the definition.
(an animal's shelter)
'here finally protected by dm's successor' is the wordplay.
'finally' indicates one should take the final letters.
'protected by' indicates putting letters inside (inserted letters are held or protected).
'dm's successor' becomes 'dn' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The last letter of 'here' is 'e'.
'e' placed into 'dn' is 'DEN'.
Can you help me to learn more?
(Other definitions for den that I've seen before include "Room for work or play" , "Animal shelter" , "Animal's lair or man's study" , "Wild animal's home" , "Hidden lair of an animal" .)