this is a ridiculous suggestion price wise, but check out custom IEMs. They are expensive as hell, but I have no issue spending money on something I use for HOURS every single day.
Those are regular IEMs. By custom parent comment means ones with a casing made specifically to fit inside your ear. Random example: http://vaiopocket.up.seesaa.net/image/sleek5.jpg, these can cost 3-4x more than a regular pair.
Have you ever had an earplug that fell out after 5 minutes?
The main reason earphones fall out of your ears is the wires. Most existing wireless earphones have some sort of wire attached to them. They're called "wireless" but that's technically not true because they do have wires, and these wires are what pulls the earphones out of your ear. It's physics.