Thats the problem grannyh, we do get complacent I put a game camera out where our coops/houses are and we have raccoon, opossum, and a big blk bear, plus bobcat foxes. coyotes. You may think you don't have preds but they are there.
It's only 10wide by 17 high, but I have seen my full grown Embden Gander go through it, but mostly they use the big door, the pop door is mainly for the chickens and ducks since we have nesting boxes in this house too. You diff want to go bigger than 10X17 since your geese will be using it for...
does your pump house already have a door? if so why not use it. our goose house has a regular size door and then a pop door for my chickens that use it for laying. the pop door is actually a kitchen cabinet front the frame and door that my dh brought home from work one day and laid around here...