Is deep perhaps but may be detected (6)
I believe the answer is:
espied
'detected' is the definition.
(I've seen this in another clue)
'is deep perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'is'+'deep'='isdeep'
'isdeep' with letters rearranged gives 'ESPIED'.
'but may be' is the link.
(Other definitions for espied that I've seen before include "Saw (archaic)" , "Watched" , "Spotted; saw" , "Caught sight of (poetic)" , "Caught sight of (archaic)" .)