The tadpoles need to be in water body of some sort, garden pond or ditch or lake. They are possible to rear in an aquarium, but there will probably be fairly high mortality. They need fairly dense plant cover and much murkier water than you would have to keep fish. They also need some way to get out of the water when they turn into froglets, so boulders or rocks or logs at one end. The little frogs, 10Ã¢ÂÂ15 mm long can be released somewhere near a relatively natural water body so that when they return in a few years time to mate and breed themselves, they do not try and get into your garden shed or whereever you keep the water tank.
Patty, I used old carpet, but you have to be very careful to get out all of the tacks and nails. The point of the underlay is to stop any sharp objects in the ground, such as rocks, stones, broken glass or shards of metal, penetrating and puncturing the butyl sheet when the tremendous pressure of the water pushes down on it. Corrugated card would probably be OK, and yes, damp it to make a good squidgy fit.
Stinky,not sure about rocks affecting the water, but you won't get much luck from returning frogs producing tadpoles if you have fish in the pond. I'd be tempted to get rid of the fish.