No. Get a decent Garmin (or equivilent) GPS which leaves a trail marking your exact path. This helps you stay in deep water and avoid any obsticles as you did when departing. The one you listed is a hiking GPS marker, I'm pretty sure.
The manual states do not store or use in areas of high temperature or humidity. The high temps and humidity may impair functionality which would seem to imply the unit is not moisture proof.
They sell a lot of those to the groups of people who do mapping work as well as "treasure hunts", "scavenger hunts" and races to far off places for fun. All they get is a set of coordinates and it's up to them to find the item. It would work for you as long as you knew the places you wanted to be, but it would still be up to you to find a way to get there.
