If he placed it on a tree, higher than ten fists, his eruv is not valid; below ten fists, his eruv is valid. If he placed it in a ditch, even a hundred cubits deep, his eruv is valid. If he put it atop a reed or atop a pole, so long as it is uprooted and is stuck [into the ground], even if it is a hundred cubits high, his eruv is valid. If he placed it in a locker and lost the key, the eruv is valid. R’ Eliezer says: If he does not know that the key is in its place, the eruv is not valid.