One dam protecting another in German city (6)
I believe the answer is:
weimar
'german city' is the definition.
(city in Germany)
'one dam protecting another' is the wordplay.
'one dam' becomes 'weir' (a weir is a type of dam).
'protecting' indicates putting letters inside (inserted letters are held or protected).
'another' becomes 'ma' (I can't justify this - if you can you should give a lot more credence to this answer).
'weir' enclosing 'ma' is 'WEIMAR'.
'in' acts as a link.
(Other definitions for weimar that I've seen before include "13 [THIRD REICH] 's predecessor" , "City of Germany" , "German city associated with Liszt and Goethe" , "German town associated with Goethe, Liszt and Schiller" , "German republic until 1933" .)