Evening,
I bought one of these for my engine:
Outboard Motor Locks
Admittedly, it didn't stop the engine going walkies one night but however the insurance paid out. I am insured with Towergate and they asked for an invoice to prove I had bought the lock. Make sure you keep all the paperwork and, to be safe, I would take photos of the fitted lock and email to your insurers too. I will do this religiously from now on.