It would be a pita to do always. But wouldn't having some sort of rod/steel tubing passing through both wheels with some sort of locking mechanism be a pretty good theft deterrent. Hitch locks are almost pointless in my opinion. Back up to trailer, chain/ratchet trap the tongue to your hitch...
Other tips:
-Have a friend there with you. Preferably sitting in the vehicle with cellphone in hand and 911 pre-dialed.
-If you have a GoPro or dash camera. Have it rolling in the direction of the transaction.
-Ask for their drivers licence(take a photo)
-Take notes of their vehicle and licence...
Lots of guys install a recluse clutch. Which makes shifting clutch less.
And even if they still have the clutch. I'm assuming they'd have enough forward momentum to allow them to switch gears.
I personally wouldn't worry to much about it. As I've never heard of them snapping.
What size are the cables? 1/4" wire rope is rated @ 1100+ lbs in a straight pull. Could you maybe increase the cable size for peace of mind?