Secure gnome — feller? (8)
I believe the answer is:
chainsaw
'feller?' is the definition.
(something which fells trees)
'secure gnome' is the wordplay.
'secure' becomes 'chain' (chaining is a kind of securing).
'gnome' becomes 'saw' (both can mean a proverb or saying).
'chain'+'saw'='CHAINSAW'
(Other definitions for chainsaw that I've seen before include "woodcutter?" , "Tree-lopper's tool" , "powered device" , "Texas massacre tool" , "Powered cutter" .)