So I have a spare key for my 2008 L322, and when I take it to the indy mechanic they just hide the key somewhere outside. I'm worried it'll get stolen someday.

From poking around and finding threads where people locked them accidentally, it seems the common way to do it is to remove the key and lock as per normal, then use the hatch button to gain access long enough to drop in the back and let the hatch relock automatically as it closes.

Is the only way to do it, or is there some other combination analogous to the old P38 "slam locking" (which doesn't seem to work on the L322)?

Just curious...

 2008 SC L322
2001 P38, Epsom Green, fully restored SOLD

This is how I did it when camping..

I had locked the car with the tailgate open. I then put the keys on the shelf at the back. Finished what I was doing and closed the tailgate. I then realised what I'd done.

I was 200km from home, in a location road service (equiv. to AA) wouldn't go. Fortunately, I'd left the front window down 30mm and was able to snake a bit of wire down to pick up my bag which had my wallet with the plastic emergency key. I lifted the bag to the gap, got my fingers in to grip the wallet and extricate it through the gap. Ron B. VK2OTC
2004 L322 V8 Auto
2007 Yamaha XJR1300
Previous: 1983, 1986 RRC; 1995, 1996 P38A; 1995 Disco1; 1984 V8 County 110; Series IIA

If I remember correctly, there is a setting in the software somewhere where you can prevent the car from locking with a key inside. Our current two runabouts in NZ (Toyota and Suzuki) won't lock when one of the keys is inside the vehicle.

So if that option is set in your cars software, you can't do the trick but like I said it can be turned off with the Faultmate (and I'm sure with the IID as well). MY 2010 5.0 SC Galway green and sand interior!!
Have the Faultmate MSV2 Extreme to be tinkering with the settings etc. !!