"live rock" is not just rock... it's all sorts of critters living in the rock. Most of this stuff is microscopic, but does need water to live. If the rock dies off, it will stink to high heaven. You wont want it on your shelf. You can keep live rock in salt water with a heater in a bucket... or trashcan. You should have a power head in there for some degree of circulation. Water changes every so often will keep your rock "live" for quite some time.