Welcome to Pond Boss!
The handbook for watershed in the area west of Ft. Worth is in the range of 12 to 20 watershed acres per acre of pond. If you have 3 acres for a 1/8th acre pond, that gives you a ratio of 24:1, so you should have enough water, not counting the "exceptional drought" years.
Are you building a house on the property? Water well or city water? For a pond that small, you could probably supplement the pond during a bad drought with water from your house to get the fish through to the next rain.
I can't quite tell from your description about how you are planning to construct the pond. Can you look around your property on the satellite view and see if you can find some 0.5 acre to 5 acre ponds in your area? That is a good approximation of the feasibility of pond building in your vicinity.
How hard was your "sandstone mess"? Could you break out chunks with your little backhoe bucket, or did it just make your bucket teeth squeal when you tried to scratch it? If the sandstone was friable (crumbly), your contractors could probably get through that sandstone layer for a deeper pond if your subsoil goes back to clay beneath a few feet of sandstone. (A medium-sized excavator has much more break-out force than your backhoe.)
Did your test hole start to fill with some water after you got down to the sandstone? How much slope is on your property? How rolling is the terrain in your county? Usually, areas called "Springtown" have some natural springs. Your sandstone layer sounds like a good candidate for creating local springs. If you did get water in your test hole then a "groundwater" pond might be an option for you.
If that sandstone was dry or impermeable, then that is not an option for you, and you will need to build the more typical "sealed" pond.
If you do have a lot of slope down to that corner of your property, then your idea for scraping up clay and building a "U"-shaped berm around the downslope side of the pond should be feasible. However, you really do need some slope to make it work. If you can only dig down 3' until hitting sandstone, then your pond bottom will only be 2' below the existing ground elevation. (You will need to excavate down to the sandstone, and then compact a 1' clay blanket on top of that for your bottom seal.)
If you are going for a 10' deep pond, then your berm will need to be 8' above the existing ground level. If you can envision a rough topographic map in your head when standing at the pond site, then everything inside that 8' high contour line will be "pond".
Also, you cannot build your pond shoreline right at the edge of the your property line. An 8' tall clay berm will probably need a 1:3 slope to be stable. That means the CLOSEST your shoreline can be is 24' from your boundary. (It will actually me more than that, since the flat part at the top of your berm needs to be a few feet wide.)
I hope that gives you some more ideas as to the best way to approach your pond construction project. I had to make many assumptions, which means that several are certainly wrong. If you clarify some more after analyzing what I said, you can probably get some better advice on the forum.
Good luck on your new pond build!
