I have had this problem.I have some DOC traps in and around the pens mate
I have also dropped the wire to the floor and have radio on and flashing lights - i now realise though these stoats will be killing out as well as in
When you find a freshly killed poult leave it where it is.
Move the DOC trap to the kill site
Put the corpse into one end of the box and block off the access so that the stoat has to pass over the plate from the other end to get at it.
(Works best when the end of the trap is wire mesh rather than solid.)
Leave it for a couple of days at least.
Only clear up when maggots appear.
If no show it has probably killed another somewhere that it is feeding off.
When you find it move the box and start again.
Works 9 times out of 10.
Most I caught doing this was 14!!! Obviously a couple of litters.
A lot quieter around the poults than a shotgun.