I still don't see a metric option with the security fasteners. I could replace the metric nut that is designed for the saddle attachment hardware but it would be jerry rigged and the nut wouldn't be secure. The existing nut is secure due to the way it insets into the hardware. The European fastener companies are also saying I need to buy bulk.

I really don't see the cable being any better than the bike chain option. The cable is easily cut and locking it creates some bulk. I tend to think that a bike chain is not as easily cut. However, anyone with a chain breaking tool can open it.

I don't really like the glue idea. It seems awkward to figure out how to soak the bolt to remove especially when it is attached to a leather saddle that could be damaged by the acetone.

I experimented with solder yesterday: that is, putting solder in the hex hole of the socket head bolt. It does seem to work -- well, kind-of. The solder melts into it okay. However, the solder doesn't remelt for removal. I think the heat is dispersing through the steel bolt and not remelting the solder. Once the bolt and solder was heated, the solder came out in solid form. I think this is because steel expands more than solder under heat.

I'm in San Francisco so I need to do my best. I thinking about duel deterrents: solder in the bolt head and chain.