Rocks and Ecstasy impounded by judge (4)
I believe the answer is:
reef
'rocks' is the definition.
(I've seen this before)
'ecstasy impounded by judge' is the wordplay.
'ecstasy' becomes 'e' (informal term for the drug).
'impounded by' means one lot of letters goes inside another.
'judge' becomes 'ref' (**).
'e' inserted within 'ref' is 'REEF'.
'and' is the link.
(Other definitions for reef that I've seen before include "Gather up" , "The sort of knot" , "Shorten sail" , "Sandbank" , "key" .)