We have a mini-Rex who lives on our screened porch. He is seldom caged, and the dogs have to go through the porch to get outside. This was never a problem with our sedate 12-year-old dog - she would just give him a little sniff hello and then move on - but when we got a rambunctious 1-year-old doodle, it was another story! So from day one with Daisy, we had to teach her that she was not allowed to approach or chase the rabbit. Fortunately, once she "got it" she's been very reliable, and we can put the dogs out with no trouble.
What I did was to take Daisy out on her leash at first, so that she was always completely under my control while we walked through the "rabbit zone". I also kept a squirt bottle of water handy, and if she rushed at the rabbit, I gave her a squirt and a firm "NO." Gradually, we introduced the two inside, with my kids holding Roger (rabbit) and me holding Daisy - again on the leash. At first we just let them sniff one another a little, but eventually we put Daisy in a submissive posture and brought Roger close and let him "claim" the dog, a la Cesar Millan. I have no idea if this really worked or if the novelty of the rabbit just wore off for Daisy, but she no longer gets excited when she sees Roger and I have no fear of her chasing him on her way outside. That said, I would never leave them alone in a room together unless I was there to supervise. She is still young and playful, and though I don't think she'd chase Roger with the intent of killing him, I think that could very well be the result if they were left alone together. The bottom line is that he's 4 pounds and she's 55!
I think in your situation, what I'd do is introduce the animals and then continue to let the rabbit have his time of free-roaming, but make sure that Gunner is on his leash and fully under your control at those times. Or, you could put him behind a gate, if that's effective for him, or in a crate - someplace where he can see the rabbit but can't approach him without your permission. Familiarity will probably eventually breed a certain amount of boredom, but in the meantime, you need to be right there and prepared to correct Gunner in whatever way you're comfortable with if he gets overly excited about the rabbit. Hopefully, they'll eventually reach the point where they can be in a room together

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Good luck to you!
S.