My wife and I have done it outside no fewer than 26 times (before I lost count). Too bad it was all before we had kids.
We were pretty daring, too. Many of the times we did it, people were within a few feet of us. Yet, we were never caught, though. We did it a few times in the open, during daylight, with cars passing a few yards from us, but they would have had to been looking specifically for us for anything to be seen.
One time, on a boat, my wife and I were with her family in the back. Everyone was sitting down facing forward and I ate her out until she climaxed...with her family a few feet away, facing the other way--and we had no back-up plan.
I could go on, but I don't remember much more.
Oh, we did do it on a golf course once. We thought it was deserted but just as we were getting our clothes back in order, a group came around the corner.