ten month old border collie has started seriously stalking our two cats over the past six weeks despite being raised with them since eight weeks, one cat now sleeps in the basement, looking for the calibrated answer on training vs management for a herding breed showing predatory drift

Wicket is our 10 month old female border collie, 35lb, working bred from a small farm in vermont where she was raised around chickens, sheep, and a couple of resident barn cats until 8 weeks. we have two cats already in the house, Pepper (8 year old orange tabby, 12lb, dominant personality, fully indoor) and Olive (6 year old tortie, 9lb, the anxious one, also fully indoor). for the first 7 months that Wicket lived with us all three coexisted in genuine harmony, Wicket respected Pepper's claimed spaces and Olive's hiding spots, they had a stable detente that we honestly thought we had lucked into. about 6 weeks ago something shifted and i'm now writing this post at 4am because Olive has been sleeping in the finished basement for 9 days and i need help.

what changed. Wicket started "watching" the cats with the intent stare we recognize from her videos of stalking the kong, low body, ears pinned forward, the classic herding crouch. it began with extended staring while sitting at the threshold of a room. then she'd creep forward 6 inches at a time when one of them moved. about 10 days ago she actively chased Olive across the kitchen at speed, Olive went up the back of the couch and over to the top of the bookshelf, and ever since Olive has not come upstairs at all. Pepper has been holding her own with hisses and a paw swat to the nose when Wicket gets too close, but she's not invulnerable and Wicket is bigger than her now and the disengagement is taking longer each time. nothing has changed in our household routine, no new people, no new pets, no schedule shift, nothing that explains why this started 6 weeks ago. the only candidate variable i can identify is that Wicket is in what working line border collie people call the "9 to 14 month arousal window" where drive consolidates.

what we have tried so far. one, redirect to a toy or flirt pole when she goes into stare, works for about 30 seconds before she's back at it. two, "leave it" cue which she has solid for food and tossed objects, works when she's already disengaging but completely fails once she's locked in for more than 10-15 seconds. three, full time leash tether to me at home for 2 weeks which functionally worked while tethered but the behavior came right back the moment she was off leash. four, structured naps in the crate. five, the herding-drive-needs-more-exercise approach where we increased her aerobic to 90 minutes a day plus mental work, which made her measurably more efficient and faster at the stalking with no reduction in frequency, which is what experienced herding people had warned me about but i had to learn the hard way. the only thing that actually disrupts the fixation reliably is interrupting it in the first 3-5 seconds of the stare, but if i miss that window she is gone and verbal cues do nothing.

what i need help understanding from people who have actually lived this. one, is this a training problem we keep working on with impulse control protocols, or is this a management problem where the dog and the cats simply live in separate areas of the house from now on, because i keep flipping between these two framings and i need someone who has been here to tell me where the line is. two, for families with a herding breed who developed predatory drift toward small household pets, what did the actual protocol look like and what was the realistic timeline. three, has anyone hired a board certified veterinary behaviorist (DACVB) for this specific scenario and was the $400-600 consult worth it. four, is this related to the 9-14 month arousal window and is there a meaningful chance it eases on its own once she is past 14-16 months, or is this a stable adult predatory pattern emerging and we should plan as if it's permanent. five, honest answers welcomed including the "we ended up rehoming the dog" or "we ended up rehoming the cats" versions if that's where this goes for some families, because i would rather hear that now than find out at month 14 that we have been burning months on something that does not resolve. willing to do real work, willing to pay for professional help, just need to know where on the spectrum this sits