We have a kiddie pool that we tested, and the chickens can get out of if one happens to jump in (maybe 8 in. deep?). As for the poo- they cannot regulate when they go, so they just go everywhere and at any time and it can be very watery. With the mess, they cannot eat their food without washing with water, so you will have almost a mash that gets flung around as they are going to the water and back. It ends up getting really stinky and gross, so you have to clean it 1-2 times a day. Also, they tend to try and fit their entire bodies into to waterer and they and up splashing water all over the place. They technically do not need a pond at all, but they are much much more happy when they do. You will also have to empty their pool 1-2 times a day or more depending on the bedding in the run, and how muddy they can get it.