Labrador, say, starts to gobble grub outside peacekeepers’ party? (6)

'labrador say' is the definition.

'starts to gobble grub outside peacekeepers' party?' is the wordplay.
'starts to' indicates taking the first letters.
'outside' indicates putting letters inside.
'peacekeepers'' becomes 'un' (I've seen this in other clues).
'party?' becomes 'do' (do is a kind of party).
The initial letters of 'gobble grub' is 'gg'.
'un'+'do'='undo'
'gg' placed around 'undo' is 'GUNDOG'.