I start tileing my new shower in a few weeks. I have gone with a moody, romantic, Carolina wildlife/swamp theme. It sounds weird, but I am a wildlife girl, and it basically means a lot of greens and natural colors and accents. 
My shower is the crown jewel. I chose square emerald green subway tile, copper and brass hardware, and a river rock floor. It is going to be gorgeous. 

I had a stroke of inspiration to put a mosaic of an American alligator on the shower wall. I saw something similar on one of those home improvement shows as a teenager and I really love the idea. I'm an artist so I started designing. 
I purchased stained glass panels in my chosen colors, and fiberglass mesh backing, and got a 22×18 inch print of my design made to follow. So far it is coming along great and looking fantastic. 

My question is, how do I make it waterproof? Can I? Or is this just a horrible idea? I really want it installed in the shower wall, not as a decoration nearby. 
I spoke to my dad who is helping me lay the tile and basically building the thing for me, and he doesn't think there is a way to do it while keeping the shower waterproof. He is very experienced and has designed and installed all of the tile showers in my childhood home, so I trust him, but I also wanted to try and find a way to make it work. 

Does anyone have any ideas or experience with something like this? Is it doable? Or not even worth trying? 
I attached the mock up image of the design, but the finished version will be very different. 

Shower Mosaic? Doable or Waterproofing Nightmare?