In Scone's seven and a half years he was only outside three times - and he really didn't like it any of them. I always had him in an X-pen, with water to drink and so on, but he just didn't like it. That's probably just as well, as I was always concerned that he'd push open the screen door and go out - but he was too scared of the outdoors to ever try it. I experimented once and left the door open while I was sitting on the step, and Scone just came up to the door frame, poked his nose out very slowly, and then ran back inside.
As far as I know Natasha's never been outside, and I don't plan to start her on it. Aside from the parasite concern (we have raccoons and lots of cottontails here), I'd be most worried about raptors. I've seen and heard hawks taking cottontails around my house. I'm sure if I was sitting with the bunny she'd be OK, but still it's a risk.