Lieutenant kept inside perfect safe haven (7)

I believe the answer is:

shelter

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

'safe haven' is the definition.
'shelter' can be an answer for 'haven' (I've seen this before). I'm not sure about the 'safe' bit.

'lieutenant kept inside perfect' is the wordplay.
'lieutenant' becomes 'lt' (abbreviation for lieutenant).
'kept inside' indicates putting letters inside.
'perfect' becomes 'sheer' (synonyms).
'lt' going into 'sheer' is 'SHELTER'.

Can you help me to learn more?

(Other definitions for shelter that I've seen before include "Sanctuary; protect" , "Place giving protection" , "Roof" , "Refuge, protection" , "Monk's hood" .)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.