Automatic door locks

[mrbond]

So, I know there's a relay kit that automatically closes your windows when you lock the doors, but is there some sort of way to set up a relay to lock the doors when the engine shuts off?
I ask because I just put an Apexi auto timer in my car, but I can't lock the doors (I have factory power locks and keyless entry) when the car is still running after I take the key out. It kind of makes the whole process useless to me, since I'll either have to wait for the timer to turn the car off so I can lock it (sometimes I'm in a hurry), or I'll turn the timer off long before it would have normally. I'd like to see if anyone has any ideas on how to set something up that would automatically activate the locks after the engine shuts off.