Maverick my Aussie pup is almost 9 months old.

We currently have the living room/kitchen area gated off, cats get the whole back of the house and the bedrooms. At night all three animals sleep in the bedroom with us, cats free, pup in crate.

Both cats routinely attempt to come out into the living areas during the day, but this dog just has zero chill. If you aren't physically restraining him he will chase the cats back to the bedrooms. If you are restraining him he squirms like a stuck pig trying to get at whichever cat felt bold enough to come out.

He never does anything to the cats. On several occasions he has "caught" one, and it basically amounts to him getting in front of the cat, the cat running into him, a short staring contest, and then the cat takes off again.

I was hoping things would improve over time, but so far they have not. I have been frequently told to "tire him out more" and those people clearly have never had an Aussie pup. He's the fucking energizer bunny.

I have also tried treats, but this is difficult, as I have no way to predict when one of the cats will make an appearance, and he will seemingly drop anything (even his Kong) to go after them.

Is there anything I can do? I've spent a lot of time around dogs, but this is the first one I've ever actually raised. Is this just a "phase" that will improve as he matures? Are these baby gates now a permanent addition to my home?

It's herding instinct.
We've got 2 herding dogs.
One a small Corgi,,the other a papion.
They try herding our cat.
She's old enough not to put up with it.

Find a cat that will kick his ass, problem solved after one encounter.

Get rid of the cats?

Wife's cat is a dumb chunky CoC violation, but I'm pretty sure she loves that cat more than me, so no dice.

My cat is chill, I actually thought he would like having a dog around to do Tom and Jerry shit with, he just can't get a break with the dog in the same room.

Guessing cats are declawed.  

Shock collar or Just let it play out.  

I have upland bird dogs and 8 ducks in my yard.  A little of both and they coexist.

My dog is an Aussie/Border Collie, occasionally the neighbors barn cat will roam over to my place, shell bark up a storm. I don't have one so she doesn't know to make of it.

I've seen her chase a coyote out of the yard, she'll face off on deer all the time, she's even stood up to moose.  She gets along fine with the chickens, but doesn't know what a cat is.

First off, you got a herding breed, and it’s going to want to herd/chase things. It’s what they do. So you’re going to be working uphill.

Second, you have to train the puppy as to what you want it to do, not what you don’t want. In other words, you need to work on teaching another behavior that is incompatible with chasing that you want the puppy to do every time it sees the cats.

Start with a cat in a kennel and your puppy on a leash. Let the puppy sniff the kennel, then start the training session.

At first, you are going to want to use really high value treats. Something utterly amazing that is only used when the cats are around. The first behavior you want to mark and reward is looking away from the cat. It doesn’t matter where the dog is looking as long as it’s not at the cat. Use a clicker or click your tongue to mark the exact moment the puppy looks away, and give the puppy a huge reward. Then wait until it happens again. And again, and again. And end the session.

You’ll slowly advance to having the puppy watch you instead of just looking away from the cats. Finally, you’ll want to move into the desired behavior (sitting, going to a mat or bed and laying down, laying on a particular piece of furniture, whatever incompatible action you choose). Make sure you have that behavior established and proofed prior to practicing it in the presence of the cats. Then, once the behavior is proofed (meaning the puppy performs the action without hesitation on command), start practicing with the cats in the room. Cat shows up, puppy should automatically look at you, and then you command it to do the incompatible behavior. If it does, jackpot reward. If not, go back a step and practice the watch command with the cats there or the desired behavior with the cats gone.

Always end each session on a high note, even if it’s a very simple command. You want the dog to finish on a ‘win’. Do not lose patience or get frustrated. Neither you nor the dog benefit when you are in a negative state of mind. Keep sessions short. 5-10 minutes several times a day are much more beneficial than one hour long session. And DO NOT let the puppy continue to rehearse the bad behavior (chasing the cats). The more often puppy rehearses that behavior, the harder the habit is to break. Keep pup on a leash, keep the cat room gated off, whatever you have to do to break the cycle. Do not punish the pup for interacting with the cats; a negative association with the cats may end up making the pup aggressive toward the cats in an attempt to make them go away. And finally, once the pup is reliable practicing the desired incompatible behavior with the cat in a kennel, allow the cat to be loose in the same room while continuing to proof the desired behavior.

I really appreciate the detailed response, I will start working on this with him.