Starts to employ dogs guarding European border (4)
I believe the answer is:
edge
'border' is the definition.
('edge' can be a synonym of 'border')
'starts to employ dogs guarding european' is the wordplay.
'starts to' indicates taking the first letters.
The initial letters of 'employ dogs guarding european' is 'EDGE'.
(Other definitions for edge that I've seen before include "Golden ingot" , "Rim or sharp side of knife" , "Intense/striking quality" , "on which one is ill at ease?" , "marginal advantage" .)