We do pack in a box and secure firmly (3,4)

I believe the answer is:

tie down

I'm a little stuck... Click here to teach me more about this clue!

'secure firmly' is the definition.
'tie down' can be an answer for 'secure' (thesaurus). I'm unsure of the 'firmly' bit.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for tie down that I've seen before include "Restrict" , "Fix; bind by conditions" , "Bind by conditions - to widen (anag)" , "Restrain with ropes" .)

I've seen this clue in the Evening Standard.

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