Aly, I know how you must feel...that you've tried so hard but the dog-cat hostility continues. I'd feel tearful, too, because I'd want so much for my pets to live in peace (well, most of the time).
I know it may be difficult but can you ACT as if you are firmly in charge no matter what happens, so it's clear to Harley that you are in charge...not him.
Sorry for sending you to an article again but this one has a couple of replies to someone who had exactly the same problem as you...including the strategies not working immediately. To control the situation of 'training' 2 animals at once...the dog & the cat...the animal behaviourist says that 2 people are needed for the training.
So can you get a friend to help you? Maybe your vet could suggest a person who'd be willing to carry out the training with you & your pets. For this info, go to: http://www.canismajor.com/dog/dogscats.html
Hope it helps.

[This message has been edited by Angels3 (edited March 26, 2001).]