Don't buy bags from the bottom of pallets. That's where I have seen the worst quality in all brands. As for rocks I found one in my only bag of wicked that I've had.
I wouldn't let one rock change your mind completely. R.O. Is my grilling lump and cowboy is my smoking lump. This has produced the best results for me.
UDS (not so U) UDD, 22.5 OTS, Coming soon: mini UDS & double barreled RFS