Hi Mike,
Actaully, I dont use any rocks in my cages. Rocks can be deadly. When I was younger and not keeping snake for breeding and had numerous cages with decor in them, I had a little zonata in a nice looking rocky cage with pine cones and etc, it was a neat looking zonata habitita, but one of the rocks had slipped and pinned him down, it killed him, I think it brokwe his neck, i found him in the morning with the rock on him like that. I was devastated then,blaming myself. But as for hides-(snakes do need them, they like it) I use paper towel rolls-( the card board from when all the towels are gone) those are great cause you can throw them away and replace them easy. Also, I use little salad type plastics for hides-(you can get them at places like office depot and such) but they work great. I just turn them upside down, you could even cut a hole in the lid and leave them like that. I know rocks look beter but its much easier to do with stuff you can throw away. If you have just 1 snake, then i'd say make it a nice set-up, nice looking habitat, use any rocks you want, just wash them with hot water and soap, even use a very little amount of bleach and let them air out and dry for a couple days before placing anything that was washed with bleach back into a cage with a snake. Well good luck,
Jeff