Waterproofing marine network will take time (7)
I believe the answer is:
sealant
'waterproofing' is the definition.
(I've seen this in another clue)
'marine network will take time' is the wordplay.
'marine' becomes 'sea' (both can mean 'of the sea').
'network' becomes 'LAN' (Local Area Network).
'will take' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'sea'+'lan'+'t'='SEALANT'
(Other definitions for sealant that I've seen before include "Material stopping leaks" , "Eg, Fermat or Napier" , "Material to prevent leakage" , "Material used for an airtight or watertight join" , "Material blocking leaks" .)