If you are going to take the rock out for a couple of days the best way would be to put the rock in a large container (new garbge can or small childs wading pool) with enough aquarium water to cover them.
Add a couple of power heads for water movement, airstone and if needed a small heater. Keep the rock in a low light area (out of direct sunlight) and it should be fine. If you left it sitting out dry too much stuff would die off and when you put it back in the aquarium it would result in a large ammonia spike.
Moby