Who is the controller of an Aura with Enchant land placed on an opponent's land?
Yes, the aura remains under your control even if it enchants an opponents land and you can sacrifice it to forbidden ritual.

from the comprehensive rules:


  303.4e An Aura’s controller is separate from the enchanted object’s controller or the enchanted player; the two need not be the same. If an Aura enchants an object, changing control of the object doesn’t change control of the Aura, and vice versa. Only the Aura’s controller can activate its abilities. However, if the Aura grants an ability to the enchanted object (with “gains” or “has”), the enchanted object’s controller is the only one who can activate that ability.


In general, if you cast the spell and the spell creates a permanent (as with enchantments, creatures, artifacts and so on) the permanent will be under your control unless the card says something different.