Beacon seeking robotics (shark cam?)


It's Discovery channels shark week next week, and I am looking into building one of their autonomous shark following mini subs.

The sub will be something like this one

Being a UAV prototyper, I've never have used any 'follow the underwater beacon' systems. Anyway, I'm looking for the simplest way for a mini sub to follow a beacon. The system will need to manage pitch, yaw and throttle (needs a minimum distance so it won't scare wildlife that it is following). Roll control would be helpful, but if it complicates things by needing advanced mixings/programming, than I can just make a bottom heavy sub (old fashioned self righting eh?).

Any help would be useful, esp. a tutorial on a simple return to home feature that could be modified (home beacon could just be placed on tracked object....does the roomba come to anyone elses mind?)

Thanks in advance! -Philip