Pete, Just after that shot was taken, my boat suffered radio failure due to the high temperature of the pool water, this was due to the B.E.C. detaching from the heat sink and it's temperature soaring which caused it to fail. At the time, I was running the pump, taking on ballast, the bec quit and left me with a running ballast pump which stuck the boat firmly on the bottom.
An electronic failsafe would not have saved the day since the radio was without power. This is where a contolled 'leak' through the ballast valve would have surfaced the boat but of course one would have to wait till the battery went flat and the pump ceased to operate. In the case of this boat, we would have all grown old waiting, due to the large capacity battery but it proves a point. If this problem had arisen whilst on the pond, we would have a boat back on the surface, albeit without power but at least retrievable. If you decide to build a small leak into your valve cam, the equivalent of a slow dripping tap is ideal. I guess you know all this but thought I would mention it anyway.
Make sure your bec is firmly attached to the heat sink of the esc because without a heat sink, the bec temperature will creep up to its cut out point. When the temperature eventually reduces, the bec will cut in again and work ok . In my case, the swimming pool water was too warm and kept it in cut out mode.
Last point, if you decide to use the boat in chlorinated or salt water, flush the tank afterwards and rid it of residue. Having said all that, 'hows that new kit coming along'?