I'm trying to figure out how deep of a stock tank/pool to buy for my ducks. I heard to get a shallow one so they can get in and out, but I wanted them to be able to swim, not just run around in a kiddie pool. They are separated from the chickens, so I'm not worried about chickens drowning. If I get a tub approximately 3 feet deep will they be able to get in and out? I can always make a ramp, but I wasn't sure how necessary a deeper pool was. Any experience?