Penny running around lake? Keep going (6,2)

I believe the answer is:

plough on

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'keep going' is the definition.
Although both the answer and definition are verbs in their base form, I cannot see how they can define each other.

'penny running around lake?' is the wordplay.
'penny' becomes 'p' (short for pence).
'running' becomes 'on' (eg when a machine is running it is on).
'around' is an insertion indicator.
'lake?' becomes 'lough' (lough is a kind of lake).
'p'+'on'='pon'
'pon' going around 'lough' is 'PLOUGH ON'.

Can you help me to learn more?

(Another definition for plough on that I've seen is " Doggedly continue".)

I've seen this clue in The Independent.

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