Don't make them too realistic (night drill.. please not at sea!), fox or you might find a greater likelihood of losing someone in a drill than a real accident. There are a number of pools which offer top notch training, waves, spray, darkness.
Madbob it's not entirely true to say 121.5 isn't monitored. Airline pilots listen out most of the time so there's still a good chance of a signal being picked up in most areas. But I'm shocked to hear this is the best that's being issued when for a couple of hundred quid you can buy a fag-packet sized 406 MHz PLB