You could also just hide a real key somewhere close to your place but not close enough to make it easy for someone to try it on doors until they find yours.
You could also put it in a lockbox in a somewhat hidden location on the property, such as underneath a deck (on a house). Though a lot of lockboxes aren't that secure; after doing a little research earlier this year, I found that the Kidde wheel ones aren't bad [1].
