fourteen month old shepherd mix who was a perfectly social puppy and developed leash reactivity at ten months that has gotten worse every month for four months and the published advice has not moved the needle, looking for structural input rather than another tip because i can see the behavior calcifying and i do not know what i am missing in my diagnosis

Birch is a 14 month old german shepherd mix (best guess shepherd and something herding, about 60 pounds, neutered at 12 months on our vets recommendation). Until about 10 months old he was the kind of puppy people describe as bombproof, we did puppy class at 12 weeks, structured socialization with 30 different dogs in his first six months across a range of breeds and sizes and energy levels, he played at the dog park three times a week from four months to nine months, he greeted strangers calmly, he walked past other dogs on leash without any issue. He was the dog our trainer used as a demo dog in classes because he was so reliably neutral. Starting at about 10 months he began to alert on dogs at a distance on walks, ears forward, body stiff, but he would recover quickly if we redirected with food and would walk past at maybe 30 feet without reacting. By 11 months he was lunging and barking at dogs at 30 feet, the threshold had collapsed inward in a way that surprised us. By 12 months he was reactive at 50 feet. By 13 months at 70 feet. We are now at 14 months and on a quiet residential street he can spot a dog two blocks away and start to escalate, and a close pass (under 20 feet) produces a full explosive reaction with lunging and screaming barks that take five to ten minutes to settle from. Off leash at the few off leash spaces left where we go (we stopped the dog park completely at 11 months) he is still mostly social with dogs he knows but increasingly avoidant of strange dogs, which is a different pattern than the leash reactivity but i suspect connected.

What we have already tried, in order. Engage disengage protocol with high value food at threshold, run consistently for six weeks starting at 11 months, the threshold continued to collapse during this period rather than improve, which i now think means we were working at over threshold for most of the sessions but at the time we did not have a way to find a true under threshold distance because the threshold kept changing. Counter conditioning with a chicken jackpot for any dog sighting at any distance, run for four weeks at 12 months, no measurable change in his reaction or threshold. BAT (behavior adjustment training) sessions with a friends calm dog as the decoy, run six sessions over three weeks at 13 months, this produced the only meaningful improvement we have seen, his threshold with that specific dog moved from explosive at 40 feet to neutral at 15 feet, but the improvement did not generalize to other dogs. A consult with our regular trainer who recommended more of what we were doing, which i did for another month with no result. A consult with a board certified veterinary behaviorist three weeks ago who put him on fluoxetine and recommended we work on a duration relaxation protocol, we are three weeks into the fluoxetine which has a six to eight week onset window so we are still waiting to see if it does anything, and the relaxation work is going fine in the house but i have no idea if it will transfer.

The questions i am bringing here because i do not think i am asking the right question of my local team. one, the timeline of the deterioration concerns me more than the absolute current state, the threshold has collapsed in a predictable monthly progression for four months despite intervention, and i need to understand whether this pattern is consistent with normal adolescent reactivity that will resolve with maturity or whether it indicates something structurally different (genetic predisposition, second fear period that we missed the window on, something else i am not naming). two, the discrepancy between his on leash and off leash behavior with strange dogs is widening, he is reactive on leash and avoidant off leash, both directions away from the social neutral he had at 9 months, what does that pattern suggest about the underlying mechanism. three, the question of whether to keep pushing modification protocols or shift to management, my partner is starting to ask whether we are putting Birch through training that is not helping him and is making us anxious, and i do not know how to evaluate that question without more information about what modification can realistically achieve at this stage. four, the question of timing on the fluoxetine, the behaviorist said we should see whether the medication helps before adding more behavior modification on top of the relaxation work, but waiting another five weeks while the threshold continues to collapse feels like it has its own cost, how do experienced people balance these two concerns. five, the question of whether i should be pursuing a second opinion, the behaviorist consult was thorough but produced a treatment plan that does not include any modification work for the leash reactivity directly, and i am uncertain whether that is the right call. i would value input from certified behavior consultants, veterinary behaviorists, and especially families who have lived through this with an adolescent shepherd or shepherd mix where the timeline of onset and progression matches what we are seeing, the published forum advice has run out of new ideas for us and i am trying to figure out whether we are missing a diagnosis or whether the current treatment plan is actually correct and we just need to wait it out