With my current wife, I usually go to a park near my house and fuck her like that. Although she doesn't wear underwear. We've been seen fucking quite a few times, but so far, no one has come near. Little by little, I'm turning her into a slut, and I'm sure if someone came near and I invited them, she'd let them participate.
There is a church with a little forest , where I take my wife, strip her, and have her walk around, while I sit on the front steps and enjoy. After a while, I place her on the car hood and fuck her for a while. She loves that church.