Marsala is available in many levels of sweetness, with dolce providing the best substitute for cream sherry. Madeira, produced on the Portuguese island of the same name, is another viable substitute. In a pinch, sweet vermouth can also be used successfully in many recipes.
First they are all concrete, just different application methods. Gunite (dry nozzle)is a dry mix where water is added at the nozzle. Shotcrete (wet nozzle) is premixed wet. They both use high air pressure to force the mixture to stick to the wall. Just as if you take a ball of mud and throw it at something, if wants to stick.
Gunite is mixed on site with cement and sand and shot through a hose where water is added at the nozzle, it allows you to shoot it in layers and allows easy shaping of the pool. 40 to 60 long X 20 is a good sized pool you are going to want to some good engineering on a pool of this size.