Laying the groundwork

i've been slowly trying to lay the groundwork to convince my girlfriend to fuck another guy or at least be naked in front of someone. i have serious doubts she will ever fuck another guy,but it's fun to flirt with the idea. the naked part might be easier. i know she likes to skinnydip and we have a spot we go somewhat regularly. usually she keeps her suit on. ive taken her top off and kissed her big beautiful breasts there before though. the river sits right next to a hiking trail and occasionally people come by but its a little out of the way. right now it would be a big thrill to just see her caught nude in front of one of these hikers. any tips anyone?