Alsatian guy with crook tails FBI agent guarding HM (6,8)

I believe the answer is:

german shepherd

I'm a little stuck... Click here to teach me more about this clue!

'alsatian' is the definition.
(synonyms)

'crook tails fbi agent guarding hm' is the wordplay.
'crook' becomes 'shepherd' (I can't justify this - if you can you should believe this answer much more).
'tails' is a charade indicator (letters next to each other) (tail can mean to follow).
'fbi agent' becomes 'g-man' (synonyms).
'guarding' is an insertion indicator.
'hm' becomes 'ER' (HM Her Majesty, ER Elizabeth Regina).
'gman' enclosing 'er' is 'german'.
'shepherd' put after 'german' is 'GERMAN SHEPHERD'.

'guy with' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for german shepherd that I've seen before include "Alsatian" , "one wearing dog collar?" .)

I've seen this clue in The Daily Mail.

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