I am only going to be stationed here about 3 years. Should i go through the trouble of digging a pond or make one out of lawn timbers? I just want something large enough for some koi
depends on your budget, if it's tight I'm afraid it's a hand dig. if you've got the money for lumber and think you'll want to transport it, go for wood.
personally I'll always dig. I can make it what ever size/shape I want without higher cost and when i leave I can just get some fill dirt if the next owner doesn't want a pond.
If more of a temp./growout situation, I would vote for wood. It is easier to move down the road. It can then be re-built and house the stock at your next house while you dig the next one.