Not keeping up with one of the symptoms of coastal erosion (6,6)

I believe the answer is:

losing ground

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'one of the symptoms of coastal erosion' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'not keeping up' is the wordplay.
'not keeping' becomes 'losing' ('lose' is the opposite to 'keep').
'up' becomes 'ground' (I am not sure about this - if you are sure you should believe this answer much more).
'losing'+'ground'='LOSING GROUND'

'with' is the link.

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I've seen this clue in The Irish Times.

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