I tried growing some calla's in the pond last year. They seemed to take off well if I set the bulbs only partially submerged (about half out of the water), but if I put them fully in the water the bulbs started to rot. Unfortunately at this level, the bulbs were guaranteed to freeze over the Winter, so I thought maybe burying them in the dirt right up against the pond liner might be worth a shot (callas will not normally survive Winter in my area, so I was counting on heat from the water to prevent freezing). Unfortunately it looks like this experiment may have failed... So far I have seen no sign that any of the bulbs survived, however the weather has been questionable so maybe they're just waiting for the real heat before they pop up.
Crossing my fingers, but hope is fleeting.