If you install a tachometric relay (as used in LPG vehicles) you can take the pulse from the distributor.
How it works is once the ignition is turned on the relay allows the fuel pump to run for a few seconds then shuts it down. This creates fuel pressure to start the engine, once started the pulse of the low tension circuit to the distributor keeps the relay operating.
Once the pulse stops (the engine stops turning over) it shuts down the fuel flow.
This means in the event of a ruptured fuel line after the pump the engine will stop and so will the pump.
Relays are avaialable on eBay and cost around 30-40 Aussie $.
I use them on modified fuel injected cars, but they will work with a carby just as well.