Sarah let out the breath she had been holding and nodded. "The crystals, they can hold things, and not just small things. It could hold it until it was released by shattering the crystal, so if the Dementors aren't solid, then the ground could work." The looked down at the crystal in her hand, then up at Lavender again. "As long as I can do it, the crystals will do anything I want."
She canted her head, considering. "Your Patronus – is it something that's made new every time you cast the spell, meaning we could replicate this over and over, or does the magic have to return to you to recast it?"
She had read the books, but there was a large difference between reading those books and what actually happened with their magic.