Originally Posted By: Mark_R
I was thinking about something that bolts or straps to the car frame and requires a combination to open instead of a basic magnetic hide-a-key.

If you have a trailer hitch one of these might work. I have no idea how secure these things are. I don't own one. But I was aware that they exist, so posting that here, with no recommendation of good or bad.

https://www.amazon.com/HitchSafe-HS7000T-HS7000-Key-Vault/dp/B000I66JEM