Staying alert in canvas shelter I've positioned by headland (13)
I believe the answer is:
indefatigable
'staying' is the definition.
(thesaurus)
'alert in canvas shelter i've positioned by headland' is the wordplay.
I cannot quite see how this works, but
'in' is found in the answer.
'by' could be 'at' and 'at' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for indefatigable that I've seen before include "Unflagging" , "Unremitting" , "Persistent" , "Tireless" , "Assiduous" .)