Snake to stop surfacing (7)
I believe the answer is:
asphalt
'surfacing' is the definition.
(I've seen this before)
'snake to stop' is the wordplay.
'snake' becomes 'asp' (asp is a kind of snake).
'to stop' becomes 'halt' (halt can mean to stop).
'asp'+'halt'='ASPHALT'
(Other definitions for asphalt that I've seen before include "Road surface material" , "Material for covering roads" , "Pitch surface" , "Roofers use this" , "Paving material" .)