IMU sensor and gps

Hi guys,

I'm building an underwater device (ROV). I'm just having some trouble with IMU. I have a 9DOF Adafruit mag/acc/gyro (http://www.adafruit.com/product/1714). I'm in the "thinking" phase, the idea is to use that IMU sensor to stabilise the ROV (also using a pressure sensor for the deep). However is interesting to know the position underwater. Obviously GPS signal is not able to go underwater, my idea is to get the position with the gps just before the dive, and also each time that the ROV go back on surface, and use the IMU sensor to "correct" the last gps-position known. I don't need a millimetric precision, but however having an approx position is also good for me.

If someone has an idea how to do that, or maybe some article where someone has already do that.

Thaaaaaaank you :=)