A few notes, with the understanding that you are new. Nullify does not protect an enchantment against Dispel. Nullify only triggers when the creature is targeted by an incantation or enchantment, but Dispel targets the enchantment itself. Also, the dispel wand cannot target Turn to Stone as I believe it is a level 3 spell, and dispel wand can only destroy level one spells.
Also, you are not sapping 8 mana per game from them. As you are the controller of Turn to Stone, you have to pay the 4 mana upkeep in order to keep it attached to that creature. If the opponent had to pay for the upkeep cost, it would say something along the lines of "This creature gains the Upkeep +4 trait" so you are actually sapping yourself of 8 mana per turn when you play two.