Wanders off (6)
I believe the answer is:
'wanders off' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for strays that I've seen before include "Wanders off, digresses" , "Goes off course" , "Wanders off with satyrs" , "Wanders off the right path" , "Wanders off the beaten track, gets lost" .)