Quote from Rezzahan »Your opponent's Song will be a land under his control, since nothing changes the controller of the permanent here. It unattaches from your creature because it is not an aura anymore nor is it an equipment. Your Song is still legally attached so it stays on. You control your Song, just like your opponent still controls his (it's just a land now instead of an aura). Control of your Rats, and both Songs never changes in this scenario. It is common practice to place an aura on the object it enchants wherever that is located in the play area, while permanents a player controls are usually placed in his part of the play area. With the aura becoming a land, it is simply moved to accomodate for this. But your opponent always controls the Song here, before an after it gets enchanted by your Song.