Sounds like you had a much better plan than I did. Of course, my excuse is that I was only 16 at the time.
Ice is very safe and effective for some tropicals (obviously not going to work for Soursop and other ultra tropicalss). When we have all our pumps running, the temperature of the property can rise 3 degrees in 30 minutes even away from where the water is being applied. It does have some limitations and reqires an initial investment, but irrigation in the dry season and a good nights sleep in the winter are well worth it in my opinion.
I have pondered an overhead irrigation system for protection but haven't really looked into it other than the one shower I created over a jackfruit tree. I wonder if I could create something with a water pump I put in my pond and use to irrigate my trees? It puts out 3000 gallons an hour which I assume is way more than I would need. I'm going to do some investigating on this as it may be something I could setup for next year.
Yes, it will work with pond water. A huge portion of the "latent heat" comes from the formation of the ice. Pond water is in the 55 degree range in this part of the state durring winter and well water is about 68-70. So, there is about a 15 degree difference. We use both and they protect the trees equally. The only difference is that there is a little more ice formation with the pond water. Greater ice formation can lead to limb breakage if it become excessive, especially on poorly trained trees with narrow crotch angles. There can be more cloggs with the pond water, but this is usually mitigated with a filter on the main line. Regardless of the water source, imitters will clog as the system ages and algae forms in the lines. As a result, checking for clogged imitters is a normal part of growing the tree.
The only concern I can think of with using pond water is if you are protecting "bearing trees" (or trees with ripe or soon to be ripe fruit on them). This should never be a concern for lychee or mango, but might be worth considering if you are also protecting jujubee or loquat with overhead irrigation. In that case the water would likely need to be tested for biological pathogens such as E. coli.
Also, some what counterintuitively, water management often has fewer regulations on pond water usage than well water in commercial settings because pond water is considered recycled. This obviously does not apply to natural water sources such as pumping out of a river or lake which often requires special permitting from the governing agency.