Just adopted a 7-year-old Frenchie with some serious resource/space guarding issues. Looking for advice on how to proceed

[u/Scary-Light6773]

My girlfriend and I adopted a 7-year-old male French Bulldog from a shelter yesterday, and I’m looking for some advice on how to proceed with some of his behavioral issues.
First off, I’m fully aware of the 3-3-3 rule and understand that he hasn’t even been with us for 24 hours yet. I know he needs time to decompress and adjust, and we’re not expecting him to be a perfect dog overnight. I’m mainly trying to figure out the best way to manage his behavior safely without making things worse.
The shelter was upfront with us about his behavioral issues. They mentioned that he was extremely defensive in his kennel and would growl, lunge, and snap at staff when they tried to get him out. They eventually found that leaving the kennel door open and letting him come out on his own worked better.
When we met him, he was initially cautious but quickly warmed up and became very friendly and affectionate. We decided to adopt him, and honestly, the entire trip home went great. He was fine being handled, friendly with everyone at Petco when we stopped for supplies, and spent the couple-hour drive home trying to get attention and pets from us.
We also have a 10-year-old female bully mix. They briefly met in our yard, sniffed each other, and he attempted to mount her. She gave him a quick correction, and afterward she mostly ignored him. We’ve been keeping them separated while he adjusts.
Once home, we let him explore and fed him. Unfortunately, we made the mistake of leaving our older dog’s food bowl out since she’s always been a free feeder. He found it and immediately began aggressively resource guarding it, growling, snapping, and attempting to bite when approached. I was able to remove the bowl, and we realized we’d need to change our feeding routine.
We had set up our guest bedroom with a bed and water to give him his own quiet space. He initially explored it without issues, but after a few minutes became extremely defensive of the room. He would growl, show his teeth, lunge, and snap when I approached, even from outside the doorway. We left him alone for the night to decompress.
This morning was interesting. When I opened his door to feed him, he was somewhat defensive but much calmer. I was able to put his food down and leave the door open. He finished eating and came out on his own, completely friendly again.
I took him for a walk, played with him, and he was affectionate and social the entire time. At one point, I had closed the guest bedroom door while he was outside, and I was able to go in and out of the room to set up a camera without any issues. He even followed me in to see what I was doing and showed absolutely no defensive behavior.
Later, after having him in the guest bedroom for about 30–40 minutes while our older dog ate, I let him back out and left the door open.
He was hanging out near the front door, probably 20 feet away, when I started walking toward the hallway to close the guest bedroom door. He immediately sprinted ahead of me and positioned himself between me and the bedroom. He wasn’t initially growling or snapping, just standing in front of me and watching what I was going to do. If I moved, he’d reposition himself to stay in front of me. When I continued toward the room, he became defensive again, growling, showing his teeth, and lunging.
What’s confusing is that outside these specific situations, he’s been an incredibly sweet dog. He actively seeks affection, enjoys walks, plays with toys, and seems genuinely happy to interact with us. But when it comes to food or what seems to be his personal space, his behavior changes dramatically.
He’s also currently intact and has a neutering appointment scheduled for October 21, although I understand neutering isn’t necessarily going to fix resource guarding or fear-based behavior.
My biggest concern right now is figuring out how to safely manage him while he adjusts.
I was fortunate enough to be off work today, but tomorrow we’re both back to our normal schedules. I work 6 AM–2 PM, and my girlfriend works 8 AM–4 PM. We have a camera set up in his room, but I’m unsure whether continuing to use the guest bedroom as his designated space is the right approach, considering how defensive he becomes around it. We also have a good sized fully fenced yard. I don’t want to repeatedly put him in situations where he feels threatened or feels the need to defend himself, but we also need a safe way to keep him separated from our older dog while we’re at work.

Any advice or personal experiences would be appreciated!

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[u/Sitters_4_Critters]

r/muzzledogs has great resources for finding a muzzle, including muzzles for brachycephalic dogs.

Michael Shikashio is a behavior expert and does a lot with resource guarding:

The Bitey End of the dog podcast is great and Michael Shikashio also has a great website with webinars and other resources: aggressivedog.com. You can subscribe for $30 and cancel anytime. I found it helpful when I had an aggressive foster dog.

Here’s where to find a reputable behavior specialist to evaluate the dog:
International Association of Behavior Consultants: https://iaabc.org/certs/members

Vets with specialty in behavior: https://www.dacvb.org/search/custom.asp?id=4709.

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