Question
I want to build a pond and have been doing some research, but there are 2 questions that are just itching me.
1- How deep does a koi pond have to be??? I know it has to be at LEAST 1000 gallons.
2-How do you plant a water lily??? I had a small no fish pond and tried to plant one using normal garden soil, a pot, and gravel on top. Within 3 seconds, the pond was muddy. What do you do?
Thank you for your time.

Answer
The depth that the pond should be does depend on where you live.  If you're in Zone 7 or higher, then 3 feet deep is good for koi so they have room to move in the water column.  My pond was supposed to be 3 feet deep but they messed up, and I got 26" at the deepest.  I only have two koi (and other fish) in my 1800 gallon pond in Zone 6/7 but the 26" has been deep enough to keep my fish alive for 9 winters.  If you are in Zone 6 or lower, then you need to add on another foot of depth or so each zone that you go down. If you're not in North America, let me know, and I'll try to figure it out for your area.  

How many koi would you like?  If fewer than half a dozen, a 2000 gallon pond should be fine.  If more, certainly bigger.  Most people regret that their pond isn't big enough (not the other way around).

My koi page leaves much to be desired (I have no time to update and expand it) but it has some good links:
http://www.fishpondinfo.com/koi.htm

I describe how I pot my plants at
http://www.fishpondinfo.com/plants/plant2.htm#descrip
Also, see
http://www.fishpondinfo.com/plants/lilies.htm#lily

I use pots without holes, clay soil topped with pea gravel.  It only puts out a little bit of dirt when I do it.  You can also buy aquatic plant "soil" like this:
http://www.thatpetplace.com/pet/prod/202600/product.web

Good luck!