Impress deeply with George in ... in shower (7)
I believe the answer is:
ingrain
'impress deeply' is the definition.
(I've seen this before)
'george in in shower' is the wordplay.
'george' becomes 'g'.
'in' indicates putting letters inside.
'shower' becomes 'rain' (synonyms).
'in'+'rain'='inrain'
'g' inserted within 'inrain' is 'INGRAIN'.
'with' is the link.
(Other definitions for ingrain that I've seen before include "Make a habit" , "Drive home" , "Firmly establish (habit)" , "Fix" , "deeply impressed" .)