Hi Madeline! I would strongly suggest no harness, leash etc. WAY too many stories of rabbits breaking their backs, it’s not a freak once in a while thing, they are very dangerous. Any rabbit can startle, they are very strong and have very thin bones. Not a good combination.
If you want him outside, I would use chicken wire or similar material to ensure there is no way to escape under fence gaps, ensure your fence is high enough. and supervise closely. Use a clicker or just cookies to teach her to come, and head outside! I used to take Rupert out in my old house and just walk around with him-no leash and close supervision. He’s comfortable being handled, picked up and will come to me and we never had incident.
Here on the acreage, even when we do fence, I am just not going to be looking for a startled bunny in the woods, so I will hopefully be putting together something of a cat house for them to spend some time outside-even covered I will supervise. Rupert is the kind of bunny who likes outdoors, but most don’t so you may find all these tips are moot point and your bunny wants to stay inside 