Hey there, Craig. Properly cured concrete ornaments should not leech enough lime to be a problem. New concrete is the worst for that. However sealing the concrete would eliminate the problem entirely.

Contacting the manufacturer is often the best way to go.

Fired clay durability will depend on the original material and the firing temp. Low temp firing is definitely less durable than high temp. Once again sealing the material will reduce problems.

There are several products out there used to seal concrete in pools and ponds and there are discussions on some. I suggest you do a search for the ones that would affect your project. I used "lime leaching from concrete into pond"and came across several.

Don't worry, leaching will be fairly low and may be completely overcome by throwing a small box of sodium bicarbonate in the pond. bicarbonate will buffer the pH to 8.3 which is just what you need.

Thank you, I finally got in contact with Ascape (don't want to use any brand names), getting in touch with them other than directly calling them was impossible. I think the only reason they put me through to the tech service is because my question was so original. They mentioned the amount of lime leeching will be minimal, the biggest problem will be keeping it standing.
The pond is being dug this Thursday, I guess I'll wait and see how much room I have in the upper pond for a water tower.