Pond in duck run?

[UGAchick]

I am trying to decide whether to give my ducks a designated run, allow them to free-range in the fenced in back yard, or keep them with the chickens. Here is the sticking point: I have two huge sinkholes in the back yard that I can easily combine into one. The finished hole would be about 8' X 20' x 4' deep.
Should I flood it and make it a pond for the ducks?
Should I enclose it in their run?
Do I need to keep the chickens away from it?
Will it get nasty/
If so, how do I clean it?

Help!

 

[Jess N Jeff]

I have a pond in my run, its about 300 gallons. I clean it weekly or it stinks HORRIBLY!!! My chickens don't go near it, but you may want to realize that some chickens are curious.