Thanks for the response. Although I understand your point though from a realism aspect, I dont agree completely. I'd considered this for the smaller, lighter animals but for the larger ones that would sink in the snow it doesnt make sense. i.e. if I cant jump over the fence while standing on the snow, neither should they.
But ok... can you make a double height fence without stacking two? Or double height gate? Having to open 2 gates is really very annoying! Maybe a variant of a door?
My other, more realistic approach is to put a roof of wood slabs to keep the snow from falling inside the pan. So far it seems to work fine.