I am yet to find a good solution to be able to lock the vehicle with the radio key inside. This is to be able to go underwater (swimming, etc) with the valet key only so nobody needs to see you hide the radio key externally.
Surprisingly, the radio key inside a tin box is still detectable. Aluminium foil wrapped around the radio key is most effective and a simple way to block the transmitter.
Locking using the radio key enables the security alarm, so re-entry with the valet key will sound the alarm. So this is not an option.
With all doors manually locked the valet key can unlock the driver door. The problem is that the rear hatch cannot be manually locked and will remain unlocked without the use of the radio key.