Errands I go/run in a military post (10)

'errands i gorun in a military' is the definition.
I can't judge whether this defines the answer.

'post' is the wordplay.
I cannot quite understand how this works, but
'post' could be 'garrison' (garrisoning is a kind of posting) and 'garrison' is found within the answer.
The remaining letters 'ed' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?