I have a parachute chord with a lock on it to the cover handles. That's just to keep the honest people honest. If someone wants to get in it, they will get in it but if you have it locked to well, it might cause just enough anger that they may cause more damage. My lock will keep little children out but won't do much to deter someone that wants to soak while I'm gone.
I look at my hot tub like a do my soft top Jeep. If I keep anything valuable in it, I'm just asking someone to steal it.
It's funny to see someone get out of their Jeep with the soft top azipperedred windows, then lock their doors. I've read stories where people will try to break into them, see the doors locked, and rather than unzip the windows to get in, they take their knife and cut the top open. Just an example of the idea that you may be inviting vandalism if you over secure.
This is just something to think about, but you have to do what make you feel good about your situation.
