Yall I have the weirdest reactive dog and I don’t know how to help him.

We literally found this dog in a trash pile. Like an actual trash pile. He couldn’t have been more than a few months old, he still had his puppy teeth, he was covered in fleas and missing half of his (very broken, tweaked) tail. After looking for an owner (obvs there wasn’t one) we ended up keeping him because he got along really well with our cat and my middle aged blue heeler GSD mix who really loves having other dog friends. This dog is probably a border collie/pit/chow mix, he’s got longer curlyish hair, doesn’t shed a ton, but a square pit face and a blue spot on his tongue. He’s about 50 pounds.

He isn’t fixed yet (I KNOW) but that’s partially because shortly after we got him, he got deathly ill with autoimmune meningitis, almost died, had to be in the hospital with a deadly fever for like four days, the whole thing. He was then on meds for almost two years and was just recently cleared to undergo surgery so the fixing will happen soon.

But outside of that, I cannot figure out what and why he’s reactive to things. He’s VERY food motivated and a little resource guardy, but he will let the cat come by his food bowl and fish little pieces out while he’s eating, it’s kind of their morning routine at this point haha. He’s bffs with my older dog and has been so kind with every cat he’s ever met, including when we’ve had neonatal fosters. He just gets down on their level and wants to lick their head. Honestly he straight up wrestles with our cat and then lays down and cuddles him and licks him lol. He’s fine with children and even lets them be a little rough with him. And I would say 8/10 times when we’ve brought a friends dog TO the house, he’s mostly been fine. Like another dog coming into HIS house doesn’t really trigger him.

Outside it’s a completely different story. He’s impossible to walk, lunges at everything. Sitting on a patio with him is miserable, any time another dog walks by it’s a WAR. Car doors beeping, pedestrians walking by the house, it’s a meltdown. He’s gotten in one real fight since we’ve had him and lost - a family member was trying to give him and THEIR reactive, resource guarding dog a treat at the same time and the two of them fought - but my dog ended up the loser with an infected bite and honestly could have effed up the other dog a lot more than he did. The other dog bit and for my dog it looked more like a warning. He’s never bit a person in violence but is a little nippy when someone walks into the door cause he gets excited, but worst he’s ever done there is rip a shirt.

Other than getting him fixed…what’s the move?? I’ll invest some money in him as I’m looking to have a baby next year and I need him to not be so loud and reactive at home so as not to wake a baby up (though again he’s met babies and kids and was fine so I’m not too concerned about that part). Any ideas?