One is defenceless on these, which the experienced know (5)
I believe the answer is:
ropes
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for ropes that I've seen before include "Lassoes" , "weaker people may be on them?" , "Ties" , "Painters" , "Onion or pearl strings" .)