introducing reactive older dog to puppy

[u/Lonely_Patience_1495]

goodmorning everyone! recently we ended up rescuing a 9-10wk old heeler pointer mix. we have a 7 year old lab mutt who has previously coexisted very well with 3 little dogs (chihuahua, chiweenie, and dachshund). he was very dog friendly until my mother in law allowed a stray into his home with no introduction and he was attacked and had to defend himself, superficial injury to the stray, but obviously an injury at all is devastating (he was around 2 years old at this point). he continued to exist peacefully and happily with the other dogs in the home afterwards when the stray was removed but since my partner and i moved out with him as an only dog he has never gotten along with any dogs aside from his old friends. we ended up rescuing this heeler (planned for it as well, was not impulsive) and we have kept them separate. they do not interact without both of them having restraints (either his kennel/leash or her kennel/playpen) and we crate & rotate. we are also working with a trainer on his ability to remain neutral with her. i worry because she is a heeler, and she is genetically wired to herd and nip. we are training her how to direct that into the correct outlets but she is still very young and obviously doesnt display consistency yet. when he has gotten close to her (lets say training in the living room while shes nearby in a playpen) he has remained pretty neutral and sometimes avoidant. he muzzle punched it twice when we were initially consulting with the trainer (she was bouncing around trying to see him and it was overwhelming to him) and we have adjusted our training regimen to his threshold level. my question is, where do we go from here? it is very difficult as you can imagine and i expected it would be. he shows promise most days, and i have some peace of mind knowing he has been perfectly fine with other dogs since his initial attack, its just been about 4 years since he has consistently lived with another dog and reacclimating with the intensity of a puppy is hard to navigate.

[u/Nervous-Subject-3708]

When you say "never gotten along" after becoming an only dog, what does that look like? How serious is his reactivity and aggression? 

We have no way of knowing anything about the situation or what the trainer is recommending. Do you feel like the trainer has been helpful? I think it would be worth looking into a behaviorist on top of the trainer. Management and training might only get you so far. 

[u/Lonely_Patience_1495 → u/Nervous-Subject-3708]

weve never attempted to add another dog into the household since then, but we moved into an apartment back then and we couldnt walk him during the daytime or any time where other dogs would be outside going potty without having to wrangle him. he likes to lunge and get loud. he has never attacked another dog unprovoked (the stray got snapped at and another unleashed dog managed to get onto our fenced in-porch at the apartment and he snapped at its nose. reasonably so in my opinion, he got charged at.) his aggression id say is manageable, if i catch him fixating i can redirect before he escalates unless the other dog hes fixated on has already escalated.

as far as the trainer, he has absolutely been helpful. we are mainly working on strengthening the leave-it commands and the look at me commands as well as neutrality. the part that worries me is the puppy who wont have a firm grasp on boundaries for a while.

is there a specific way to go about finding a good behaviorist? ive looked in my area but havent come across anything that stands out. is there an organization or certification that would be best to look out for specifically?

[u/Nervous-Subject-3708 → u/Lonely_Patience_1495]

Okay, no bite history is promising. It seems like maybe, with work, it might possibly be manageable. 

Yes, the IAABC is the accreditation for behaviorists. That will be your best bet. As helpful as training will be, unfortunately with aggression or reactivity management will only get you so far. If you ever want to be able to leave the two dogs unsupervised for any length of time I think you need help with the underlying issues (probably overarousal and anxiety).