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?
He was pissed due to the no call on the hit he received. I'd tell him to take the remainder of the season+playoffs off and we'll re-evaluate in the summer.