Amy, you will have to decide on what you do at night based on the predators. If shutting them in the doghouse is the only way you can keep them safe at night, then that is probably best. But, ducks and geese don't sleep at night like chickens, and won't really care to go in a doghouse at night. They prefer to hang out in the open, even in the worst of weather.
Chickens kind of go into a trance at night. It takes a lot to even wake them up. Ducks, on the other hand, cat nap day and night and the rest of the time they are up chasing bugs and having a great time. I hardly ever catch my waterfowl asleep at night. Nighttime predators are pretty deadly, though.
You really should consider a fence. Not so much to keep them in, but to keep predators out. And yes, they will hang out ON the water at night if they are given the chance! They are more wakeful than chickens, but they are just as helpless since they really can't fly. (Most of them)
DeAnna