Cover that prevents damage to the sewer (7)
I believe the answer is:
thimble
'cover' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for thimble that I've seen before include "sewer cover?" , "Belt him (anag)" , "Caucus-race prize (Alice)" , "digital screen" , "Cover for finger when sewing" .)