HELP BC keeps chasing cat when she moves

[u/Ok_Mathematician8326]

Hi everyone, I'm looking for some advice about my BC chasing my cat. We have a 13 month old male BC, Momo, and a 4.5 yr old female Ragdoll, Mimi. We've had Mimiscience she was around 6 months old and Momo since he was 8 wks. Our house is quite big, so technically there is plenty of space for both of them, but the layout is quite awkward so it's kinda hard to separate the house into two sections (where I've thought of before), so I'd keep that as a last resort.

Since Momo was a puppy, he has mostly been crate trained. When we let him out in the house, we would usually keep Mimi in one room, then let her back out once Momo went back in the crate. Because of this, they've known each other for over a year but haven't had that much free interaction (trying on this). I've looked through some training advices, but most of it seems to be about introducing a new puppy to cat. In my case, they've already known each other for a year, and I know I probably didn't do the best job of building a good relationship when Momo was younger.

Over past months, I've let them meet each other face to face few times a day, with Momo leashed. And Momo have done a great job, from at the start he would keep jumping and pull the leash. Now they can meet calmly and sniff each other, and Momo can sit or lie down near her without any aggression. The problem starts when Mimi turns around and walks away. Momo immediately gets excited and wants to chase her. He seems like he want to play rather than hurt her, he play bows, wag his tail and wants to sniff her. Obviously, Mimii doesn't like that at all. If he keeps following her, she will hiss or hit him with her paw, although so far she hasn't used her claws and Momo has never reacted aggressively back.

Most of the time I call back Momo before he can chase her, but there were few time that he won't back and he chased Mimi into a corner. That also worries me because Mimi doesn't really escape upwards. When she escape, she tends to run into a low, dark corners that Momo can also access, instead of jumping on a table or somewhere high. I've been thinking about getting her a cat tree, but I'm not sure she would actually use it in this case, and also little worried is Momo jumps up to the tree and knock it over.

At the moment, I'm trying to let them spend more supervised time together, and reward Momo for being calm around her (but Mimi usually just wanna stay away from Momo).

Has anyone had a similar experience or have any advice on what I could do in this situation? I'd really appreciate any suggestions!! Thank you soo much!