Please excuse my ignorance but are you using a type of detector/device to find the coin? 80cm is about 31" and I don't know of any device that will recovery a coin at that depth.
I am an independent Iranian researcher, inventor, and developer of specialized chemical formulas for surface exploration and metal identification. I am also the author of a research paper documenting my work and field experience.
Unfortunately, due to extensive sanctions against Iran, limited access to international scientific networks, and the difficulties I have faced in my own country, I have not been able to establish meaningful connections with the United States to present and further develop my invention.
You are welcome to visit my Instagram page,
@AurumLocator, where I demonstrate the entire exploration process, from preparation and operation to real field searches and findings.
My hope is that one day I will have the opportunity to bring my invention to the United States, conduct further testing, and develop it through scientific collaboration and practical field research.