He gets a countermand to stop at sea (5,2)
I believe the answer is:
heave to
'stop at sea' is the definition.
(I've seen this before)
'he gets a countermand' is the wordplay.
'gets' says to put letters next to each other.
'countermand' becomes 'veto' (I can't explain this - if you can you should give a lot more credence to this answer).
'he'+'a'+'veto'='HEAVE TO'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for heave to that I've seen before include "Of ship, stop without anchoring or mooring" , "(Of a sailing vessel) stop moving" , "stop at sea" , "come to a stop for navy" .)