I have a dry bag (like the one's here on catsailor) that has a lanyard string on it. I attach the lanyard to the shoulder strap on my PFD and put some sticky back velcro on the back of the dry bag. I secure the GPS with the velcro to the chest/shoulder of my life vest high but within easy reach. It rarely looses contact with the sky that way. The string helps in case I have an 'oh $hit' moment with the GPS in my hand or in case it gets knocked off the velcro.