More guarded retro dance that’s marking year’s end (7)

'more guarded' is the definition.
Both the answer and definition are comparative adjectives. Perhaps you can see an association between them that I can't see?

'retro dance that's marking year's end' is the wordplay.
'retro' says the letters should be written in reverse (retro is Latin for 'backwards').
'dance' becomes 'reel' (reel is a kind of dance).
'that's marking' becomes 'ie' (I can't justify this - if you can you should give a lot more credence to this answer).
'end' says to take the final letters.
The final letter of 'year' is 'r'.
'reel' back-to-front is 'leer'.
'leer'+'ie'+'r'='LEERIER'

Can you help me to learn more?