Dumbledore merely touches the wall of the cave and says:
“This place has known magic.” 
My home and garden too, are magical places. And magical places attract all sorts of energy, both light and dark. Stronger warding is necessary. I purchased an entire pallet of Selenite slabs to be spaced around the entire boundary of the property. (This was an investment – I’ll just say that.) The boundary was then woven and connected to the central stone. The stone was placed energetically, and not quite in the center of the garden, but that’s where it needed to be.
The entire coven as well as some of my students came out to spend 4 hours setting, charging and connecting the stones. The Ward is up, no evil shall pass into this little slice of sacred paradise.