Spot keeping dog safe (6)
I believe the answer is:
secure
'safe' is the definition.
(I know that safe can be written as secure)
'spot keeping dog' is the wordplay.
'spot' becomes 'see' (both can mean to notice or observe).
'keeping' means one lot of letters goes inside another (some letters kept inside).
'dog' becomes 'cur' (a cur is an aggressive or scruffy dog).
'see' placed around 'cur' is 'SECURE'.
(Other definitions for secure that I've seen before include "lock" , "Free from danger or risk" , "Reliable; firmly fixed" , "Firm; safe" , "'Safe, confident (6)'" .)