im planning on putting in a 300 gallon stock tank for my duck and goose to swim in. it will be buried up to ground level and their will be a stone wall around 3 sides. the other side will be open for them to go in and out and their will be a ramp. all my birds share a large run together so should be worried about my chickens walking in and not being able to get out? has anyone ever had a chicken drown?