We certainly will keep that place in a state of watchfulness (7,3)
I believe the answer is:
weather eye
'state of watchfulness' is the definition.
'weather eye' can be an answer for 'watchfulness' (synonyms). I'm unsure of the 'state of' bit.
'we certainly will keep that place' is the wordplay.
'certainly' becomes 'aye' (both can be used to answer in the affirmative).
'will keep' means one lot of letters goes inside another.
'that place' becomes 'there' (as opposed to 'here' meaning this place).
'aye' enclosing 'there' is 'athereye'.
'we'+'athereye'='WEATHER-EYE'
'in a' acts as a link.
Can you help me to learn more?
(Other definitions for weather eye that I've seen before include "Vigilant attentiveness" , "vigilance" , "Watchful people keep this open" , "One uses it to keep watch for developments" .)