Whenever my cat comes inthe house, my dog heads straight for the cat and chews her ears. The  cat seems to enjoy it to begin with but then gets cross as the dog somtimes gets carried away. I have tried eveything to stop the dog, eg. firm 'No' , distraction with toys etc. But nothing works! what can I do?

Cats are mostly well equipped to deal with unwanted attention.  It may be worth getting the cats ears checked to make sure there's no medical problem that's attracting the dog (and therefore he's providing some relief for the cat).