Hi, not had issues with it coming off either, but we were advised to avoid using moisturiser etc on that arm for 48hrs before applying, they also said fake tan can make it less likely to stay on, and advised shaving if you have hairy arms (but no idea if any of these apply to you of course!!).
I've found the best application site to be the back of my arm, but slightly in towards my torso, so when my arms arm down by my side the inner edge is almost hidden as the sensor is towards my torso. I know lots of promo pics have people wearing the sensor on the outside of their arm but we were told the back. Also to rotate sites, not only arm but also site on the arm. So I'll sometimes have it closer to my elbow, sometimes closer to my shoulder. Always more than a hand's width away from my elbow or shoulder though. Lastly, after I apply it I do go around the adhesive patch from the sensor itself and gently rub it to make sure it has properly attached. I find it hard to get off after two weeks inc in this warm weather and with daily showers and exercise, but there if you search for libre on here there are threads of other tapes or straps etc people use for sports for example.