Well its simple I suggest that we run guild dungeon only when we're sure in our victory and also I suggest to set a date when we would run it so people can prepare and make their plans.
Also I suggest to run guild dungeon when we have double force then our enemy for example level 1 guild dungeon has 60 000 force in that case we should use 120 000 and we won't suffer any loses.
In extreme situations like guild dungeon timer run off soon we could make an compromise and run it with not that big army.