cat aggression towards dog

Question
We recently adopted a 2 year old male, gray/white shorthaired cat from a shelter. He is very calm, friendly and loving in nature. We know very little about his history prior to being at the shelter. We also own an 11 year old Siamese male cat, an 8 year old female Bombay/mix cat and a 5 year old male, black labrador retriever. The 3 cats seem to be getting along pretty well so far and it has been just 3 weeks since the newest guy's adoption. As far as the dog is concerned, the new cat has been very fearful of him and displays this fear with lots of hissing, spitting, and sometimes growling which then leads him, (cat) to flee the room entirely. The dog has not approached the cat at all and does very little to provoke the situation. Just today though, things ramped up to the next level and the new cat became very agitated and actually lashed out at the dog with his claws and then kept running around to get in front of him as if to block the dog's access to wherever he was headed towards, ie: the back door to be let out, the room where the dog's food bowls are kept, etc. My dog reacted very sheepishly and backed off each time the cat came towards him. I'm not sure what to do at this point as I don't want to make the situation worse. When this scenario happened earlier today I instinctivly reacted by clapping my hands loudly at the cat and then grabbed the water bottle which sent the new cat scrambling upstairs. (The dog does not have access to the upper level or basement of our house). So the cat does have plenty of access to "safe zones" around the house...so where do I go from here? The fear issue I understand would probably just be a matter of time and patience but the aggression has me a bit worried and I want to nip this in the bud before it gets out of hand and someone gets hurt. Thank you in advance for any helpful advice/ideas in this matter.

Answer
I feel your pain! I'm in a similar situation.

Keep in mind that your new dog is frightened, and probably doesn't wish to cause any trouble--which is why he's backing off, when he could just as easily tear the cat open.
Your cat also has good reason--he's probably more scared than the dog! Since neither pets are particularly young, it may take patience to overcome the obstacles, but I think you can do it :)

My first suggestion, is to buy a crate for both the cat(or cats) and the dog.
To negate any tension or jealousy, place the crates in opposite areas of the house and feed them in the crates. Also let them sleep in the crates, to avoid any unsupervised "fighting" at night.

Secondly, let the dog sniff around him some, without fear of being hurt. Hold the cat, and let the dog gently sniff him, while gently coaxing them both, with soothing words.
And then, vice versa. Hold the dog, and let kitty sniff it out.

It may help to give the kitty some "alone-time" also. Take the dog for a walk, or just leash him up outside and hold your kitty for awhile. Let him know you still love him :)

If your other cats are acting normally towards the new canine companion...you already have a leg-up. Generally felines follow one anothers' lead.. So your new cat will take a look at how the other felines in the house look at your dog...and assess whether or not he's a threat.
I wouldn't be surprised if this problem works itself out, the more your cat reasons with it...but on the safe side, make sure they're always supervised. If you're not going to be home, or even if you're headed to the bathroom or taking the garbage out, pen them both up(it's important that you don't just pen the dog, or just pen the cat. Penning them both will let them know that neither is pack leader, but rather, you are).

Hope it all works out.... :)
SC