bolt lock question?

hey guys, needing some advice. I made my dad a fishing rod holder for the rail system for fathers day. He love is, but hes afraid that someone may steal it so he wants a way to lock it down in the rail system. I used the eye bolts, into the square nut things (cant remember what they are called but found them in the rail attachment thread) into the rail system. Trying to decide the best way to do this. Im kind of at a loss, and im sure it could be a simple solution. I also dont want it to be a huge masterlock between the two eyes, unless that is the only option.


any help would be great! thank you in advance.

 

Even if you figure out a way too lock it, someone can just remove the reel from the rod. Don't take your eyes off your gear.

 

he wont have the rods in at all times, but wants to have the rod holder in at all times, just for a whim of a trip

 

I see. The only thing I can think off is to drill a hole in the channel that a master lock can fit through.
That would prevent someone from being able to slide the Tee Nut to the opening and remove the device.
Or put a stop screw and nut in the channel that would accomplish the same thing.