Soldiers kept permanently on their toes? (8,4)

I believe the answer is:

standing army

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'their toes?' is the definition.
I can't judge whether this definition defines the answer.

'soldiers kept permanently on' is the wordplay.
'soldiers' becomes 'army' (group of soldiers).
'kept permanently' becomes 'standing' (I am not sure about this - if you are sure you should believe this answer much more).
'on' means one lot of letters go next to another.
'army' put after 'standing' is 'STANDING ARMY'.

Can you help me to learn more?

I've seen this clue in The Globe and Mail.

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