Loveschild do you believe in a non-fundamental Christianity.You sound like you might believe an occultic interpretation of the Bible.
I do not believe the devils have placed boulders for they have no power to do so for there is nothing that can hinder God's operation among mankind except a person saying they do not believe.
If a person wants Christ there is no power that can hinder them from having Christ in their life.
The Bible says nothing can separate us from Christ.
If you are talking about the world being hindered because of boulders,that is not so,for God is granting them the ability to repent and be right with Him so nothing can hinder that.
Satan is only an angel and the saints are more powerful than Him for greater is He that is in us than he that is in the world.
Nothing can hinder God's operation on earth except a person not wanting to believe in truth,and even then God will still have a say so in their life in the long run.
Matt