Rule about dry ice or potassium structure (11)
I believe the answer is:
latticework
'structure' is the definition.
(latticework is a kind of structure)
'rule about dry ice or potassium' is the wordplay.
'rule' becomes 'law' (law is a kind of rule).
'about' is an insertion indicator.
'dry' becomes 'tt' (abbreviation for teetotal).
'potassium' becomes 'K' (K is the chemical symbol for potassium).
'tt'+'ice'='ttice'
'law' placed around 'ttice' is 'latticew'.
'latticew'+'or'+'k'='LATTICEWORK'
(Other definitions for latticework that I've seen before include "decorative topping for fence" , "crisscross effect?" , "grating" , "Criss-crossed arrangement" .)