Hi everyone! Sorry in advance for the long post.

Hoping if I throw this out into the world, we might get some good advice back. So here goes nothing.

We recently rescued a dog from our neighbor. Long story short, this pup was dropped off at our neighbor's house and was told "he's your problem now" 😕 Our neighbor has never had dogs, and can't nor does he want to take care of him. He was constantly letting him run free in the neighborhood, hoping someone would take him. When he wasn't roaming the streets, he was being kept in a very cold garage, with little food and water, covered in his own feces. After a few weeks, our neighbor was getting ready to load him in his car with a shotgun and take him out to a field. My husband and I would not let that happen, so we adopted him.

We already have 1 dog (my 14 year old shih tzu, Leo), and 2 maine coon cats (litter mates/brothers) who are about 2 years old. Now we have our sweet Bear, who is believed to be about 1 year old and is a yellow lab/black mouth cur/pitbull mix. (This according to previous owners and confirmed by the vet)

Now, even though Leo is old and smaller, he's very good with animals of all kinds but especially big dogs. He grew up on the rescue ranch I worked at, and got to play with dogs of all kinds, cats, chickens, horses, pigs and even a wolf. He also grew up around my parents' great danes and various rescue mutts. So needless to say, he's good. Right now, he's just needing to establish his own boundaries with Bear (like not licking his privates, or tramping all over him). Leo is not aggressive, at all, but when he plays, he shows his strength through his voice, being that he's smaller.

Our cats however, are not about it. Our one maine coon (Obi) is shy, but curious. He's tolerant, but still kind of scared. Our other Maine Coon (Apollo) however, is not having it. The first few nights, we gave the cats their own room (complete with their food and water, cat trees, toys, litter, etc) and just simply put a few of Bear's things in there to get them familiar with his scent. We slowly started to introduce the cats to Bear. However, Apollo just goes into straight attack mode. Bear would be laying on his bed, chewing on a bone or sleeping, and Apollo will unprovokingly attack him.

I should mention, the cats and Leo are all fixed, Bear is not. Bear cannot be fixed until he has his next set of shots in 2 weeks.

We've been trying to integrate them little bits at a time. A few times, they've managed to co-exist but then something gets into Apollo and he feels the need to just attack him. To which Bear, naturally, becomes frightened. On one occasion, Bear tried to fight back after being scratched pretty bad. So now we've just been keeping them seperated completely.

We even got one of those cat-calming diffusers (feliway?) And put that in their room, but doesn't seem to be making much of a difference.

Does anyone have any suggestions? Will this just take time? It's been almost two weeks since we first got Bear. I mean, I figured it would take time but... How much time until it's determined that they're just never going to get along? Also, would getting Bear fixed help with this aggressiveness? I know Bear is quite hyper being still kind of a puppy and not being fixed. Can cats sense that kind of thing?

Normally, our cats are absolutely PERFECT. When friends bring their dogs over, no issues. When people come over, the cats love the attention and new faces. But with Bear in the house, Apollo specifically, is just not having it.

We've already grown attached to Bear and would HATE to have to re-home him. However, our cats came first. 😔 Any advice would be very much appreciated! Thank you!!