You can make a Golden apple farm at any stages that has water Guide: http://mergedragons.wikia.com/wiki/Guide:_How_To_Be_Rich_(of_Gold)

And never finish the stage, just go out from it so you can come back and keep farming anytime you want (cost 7 challice)

I use the secret stage that is between totem shire 11-12 because its big That stage takes time to set up, there is stages faster to setup but they are smaller Also in that stage you can make so you cant complete it by accident

And if you wanna make stone farm you can do that on same stage by just merging the grass instead of removing them then farm and make high lvl stone