Glen - That is the other reason I cover mine at night .... to keep the Cuban Tree frogs from laying eggs in my 2 above ground small 35 gallon round pre-fab ponds. Some still manage to get in, but not very often. The illegal introduction of Cuban Tree frogs that are quite large .... and are HIGHLY invasive here since they will eat the other frogs which is believed to be the cause of loss of toad frogs as well as native tree frogs here in Florida. I get so excited when the rare occasion happens and I actually see a toad frog. There used to be lots of them here when I moved into my home 20+ years ago. Now it's a rare sight to see one. It makes me sick!
As far as a shallow pond, try using large shallow containers like the plant saucers and bury them to the rim in the ground. It might work, just make sure that you keep the water level up so it doesn't dry out. Place them in a shady area of your yard.
I love the native frogs of Florida, but the Cuban Tree frogs have all but eliminated many of the different species. It's really sad! You are lucky that Australia is so much more strict about such things. Florida is stricter now, but it is too late. They've already thrown the baby out with the bath water (so to speak). (sigh)
