Forum:Field spell card

hello guys please help me, the ruling says: If it is Set, and there is already a Field Spell Card on your opponent's side of the field, that Field Spell Card is not destroyed. But what happen if i set, Do remain the my oponent field card active, or isnt?? a mean i give you an situation, if my oponent has activate the secret village of spellcaster and he has spellcaster and i don´t have anyone, and i have sanctuary in the sky in my hand, ok after i set sanctuary in the sky, the secret village of the spellcaster remain active on the field??? that´s mean that after i set my field i cannot activate my new field card, please answer me, and explain me very well with detail, what is the situation?? it´s very important for me.