(adapted from a recent post below)
if you want to learn about dirt, see if you can make it work, but don't necessarily want to redo your Uro cages (just yet), then just play with it on the side...
try and do a sample setup. once again, not all dirt will work, so get a couple of five gallon buckets of your dirt of the day, a couple of tanks or rubbemaid bins, and "setup" a cage. add water, mix it around, dig in it, burrow in it, play in it, see how it "works". get it real nice, with some good long burrows up to your elbow, and leave it sit until tomorrow. or next week.
add a basking spot, some wood stacks, some hidespots, see how the temps are affected, and how they affect the soil and setup.
see if it crusts up, see if it dries up, see how much water you have to add, adjust or play with your venting. give it a week, see if anything sprouts. just LEARN about dirt and burrowing with your little dirt laboratory, and try different soils and mixes to see what works for you (and in your mind, for your Uros).
we tried some decomposed granite intially that dug and mixed really nicely when moist. when it dried overnight though, under the basking lights, it was like concrete, and just about inpenetrable. whoops, no good. we went with a lighter, smoother decomposed granite (and our current choice) and it worked great. digs and holds great at all stages. i would still like to get some of the 1/4 to 1/2 inch rocks out, but we have too many cages, and too much dirt, to realistically screen it. if i had only six setups, i would screen it for sure and make it even better.
a lot of lizard husbandry breaks up in threes. for successful breeding (for monitors, and i would suppose Uros) a third of the effort goes into raising a viable, socialized group of babies. a third of the effort goes into taking those into maturity and getting them to breed and lay eggs. and a third of the effort goes into the incubation (yeah, a third, there is a lot of nuance and detail to successful incubation).
on a small scale, it is still similar to the thirds. a good soil (substrate) is only about a third of the equation to having a healthy lizard (monitor, Gila, Uro, whatever). it is not the whole picture by itself, but a good substrate is a SIGNIFICANT part of the process, and cannot be overlooked.
if you guys think this soil thing is maddening, there is SO MUCH MORE to cover for lizard theory! this is only one aspect! we could get 50 people on this forum going well with soil, and a year from now, everyone being "substrate experts" we could literally start again from square one on socialization, sexing, grouping, and breeding behavior. truly, there is a monstrous amount of information to discuss. by no means do i think that changing substrate ideas completely addresses the shortcomings of captive Uro breeding. i think the captive Uro hobby could jump light years ahead with more discussion and exchange, but we can only tackle one piece at a time. dirt, soil, and substrate is actually one of the easier topics 
thanks for hanging in there
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robyn@proexotics.com
