It depends on the kind of clay and it's water retaining capacity. If it is not all clay with no intrusions it won't work. If critters can dig through it it can leak. Gophers would sink your project in a hurry.

In any case, lots of prep is involved. Just digging a hole would not be satisfactory. There have been some conversations about such a project and what is involved on this forum and there are many sites available about using Bentonite clay lining on the internet. You should do some research in advance and figure your cost as well.

Did your lot perk when it was tested before the house was built? If it did, you may need to bring in Bentonite or use a liner. Do you know how deep the existing clay is?

don;t know what you mean by "perk" we bought the house about 7yrs after it was built, we are the 2nd owners.

furthest i've dug is 2' when i was replacing parts of the wooden fence blown down from the big hurricane that came through about 2 years ago. we're about 12 miles from a major river, and are in the 100yr flood plains. i'm guessing the clay is pretty deep.

there are some large acreage ranch lots nearby that have ponds about 100-200' diameter. i'm guessing they just dug out the clay and let the rain fill it up over the years. during last summer's drought all those ponds got very low, but we've been getting lots of rain the past 5-6 weeks and they've filled back up.

i'm on a corner lot, at the back of my backyard there's kind of a shallow (2-3" deep)channel that a lot of run off comes through and out the side of my yard out to the street. i was planning to dig a small retention pond, mainly to collect the water and use the water to water my plants during our hot and dry summers. we have flash flooding on the streets during heavy downpours.

"Percolation test - Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/Percolation_test
A percolation test (from percolation, colloquially called a perc test) is a test to determine the absorption rate of soil for a septic drain field or "leach field"."

I don't know what kind of drainage system your part of Houston has but a perk or perc test is a good start to your preparation. I understand about the runoff. We used to live in Texas. Really different for someone raised in the mountains. Can you ask your neighbors if they used native clay or added Sodium Bentonite? Allowing it to dry out would be a no-no for a pond with plants and fish so your native clay may not be good enough.

There are a number of videos on youtube for Bentonite lined ponds. You can at least get an idea of what is involved in making a clay lined pond. In general it is easier and probably less expensive to line a small pond as you propose with EPDM. Why exactly do you not want to use EPDM?

A bowl shape with sloping sides is probably a good bet for you purpose. A straight sided clay lined pond is much harder to maintain but there are many examples of old clay lined canals that are still in existence after a century or more. It all depends on proper material, compression and exclusion of foreign materials. If that is not done correctly you have wasted a lot of time and labor, not to mention money.

since it'll be another month or so before i plant my citrus trees. i dug some of the dirt/clay out from one of my tree holes yesterday. it had rained yesterday morning. i dug down about 1.5' the hole is 3' diameter. about 30mins later it was about half full of water. this afternoon it is full. we'll see how it holds.

Just a question, was the hole filled by the rain or was it filled by groundwater? If it was the result of high groundwater levels, remember that water that seeps into a hole will also seep out when the groundwater level drops.

A pond only works if it has a stable water level, clay ponds will tend to be up after rains and down fast during the heat of summer. It would be awkward to find when its stocked nicely with plants and fish that the water level plummets during the heat of Summer, you would have to empty everything out and think about starting again with a liner...

There is a Conservancy movement for developing clay ponds in England that might be helpful to you. Dewponds have been common there for centuries but many were lost to development. The art of Dewpond construction is being renewed there and they almost have it down to a science.

Search subjects that might interest you are Dewpond, Million Ponds, puddling, puddle+clay, Britain+clay pond,canal construction+clay and on and on. There is a wealth of information ranging from the dewpond to Hoover Dam on the net. If you are interested, you could spend a good many years studying the entire range of information.

Since that can go way too far for your needs, I suggest the dewpond sites and checking with the local EPA office to avoid any problems and the local Cooperative Extension Service for possible tips. It occurs to me that there is at least one pond and watergarden club in Houston and probably more since we moved from the area many years ago.

Here is a link that might be useful: Million Ponds Conservancy