re: How to get a pond to retain water.....

if your ground is too silty you will have a hard time holding water unless you have something close to 20% clay. if you do have something close to 20% clay you can "fatten up" the clay by adding salt (think table salt). sodium makes the clay particles "swell up" and repel each other. calcium/lime that you see used in construction projects does just the opposite, it makes your soil more granular. the sodium seals up the micro-pores in the soil matrix that cannot be controlled mechanically. they are being sealed up chemically. get a soil test to find out how many lbs of sodium you need per square yard. if you go over this amount you run the risk of having a saltwater pond.
i have done this successfully in the tunica hills.