Spiked Sprinkler Head Hide-A-Key
Not that a good ol' rock doesn't still work just as well, but this sprinkler head version of the hide-a-key expands the options for people who have more grass than stone cover in their yard. The lockout preventer has a spiked end that presses into the lawn with no digging required. Inside, the capsule is water- and moisture-proof, and virtually indestructible on the whole.
Sprinkler head hide-a-keys are made from actual sprinkler head material, and blend in well with other, functional sprinkler heads in the yard.